Made available in DSpace on 2017-07-10T19:24:08Z (GMT). No. of bitstreams: 1 Denise_ Palma.pdf: 3977847 bytes, checksum: f1b9e703a33e6b3a240867b86778aaa2 (MD5) Previous issue date: 2016-02-17 / The wastewater of cassava industry is a resultant effluent from the processing of cassava starch extraction and has a high pollution potential due to its high organic load concentration. Its treatment via anaerobic digestion, in addition to removing organic matter, enables biogas and biofertilizer production. However, the anaerobic system efficiency requires control of alkalinity to keep appropriate levels of pH for methanogenic activity. Alkalinity monitoring is required because its wastewater from starch manufacturer has high potential for acidification, due to the presence of high concentrations of fast fermentation of sugars. This feature can be responsible for increasing acidity levels and can cause problems for methanogenesis. Some chemicals may be applied in digesters in order to provide alkalinity to the anaerobic environment. However, some of them cause problems for digestion or digesters. Thus, in order to avoid these problems, this study tested the effects of different amounts of dolomitic limestone on an anaerobic treatment system of wastewater from cassava industry. Two horizontal-methanogenic reactors with a useful 3.38-liter volume were studied. The relation between mass of dolomitic limestone and working volume was 1:2 in the reactor A and 1:4 in reactor B. The limestone were standardized so that they had diameters varying from 9.5 to 11.2 mm. They were arranged in the initial portion of the reactors, where wastewater came through. After the stabilization period of treatment systems six volumetric organic loads were consecutively applied (2.30; 3.01; 4.31; 5.69; 7.71 and 8.54 gCOD.L-1.d -1), with their respective hydraulic retention times (4.02; 3.07; 2.05; 1.69; 1.69 and 1.13 days). It was observed, for each increase of volumetric organic load that both reactors required the same period for stabilization. The statistical results of the studied parameters (pH, partial alkalinity, intermediate alkalinity, total alkalinity, volatile acidity, ratio VA/TA, ratio IA/PA, calcium, magnesium, volatile organic acids, chemical oxygen demand, number of total solids, biogas and methane, nitrogen, phosphorus, potassium, copper, zinc, nickel, iron and manganese) showed that there were significant differences between the two reactors (based on ratios of the tested limestone) only in relation to Mg2+ and TS. However, there were significant differences between the organic loads applied in each reactor in relation to parameters such as PA, TA, VA, VA/TA, Ca2+, Mg2+, removal of total COD, removal of filtered COD, TS, TFS, TVS, biogas production, methane production, and specific methane production. These differences indicate that the best results regarding the main monitoring parameters of an anaerobic system occurred in treatments 2.30, 3.01 and 4.31 g COD L-1 d-1, with pH values above 8.0; higher concentrations of alkalinity due to bicarbonate and total alkalinity (above 1500 mg CaCO3 L-1). These data closely matched to the highest concentration of magnesium ions in the effluent of reactors (67.28 to 114.90 mg L-1); COD removals were above 90%; methane percentages in biogas varied from 73 to 76%; the highest averages of specific production of biogas were from 0.31 to 0.49 Lbiogas g CODconsumed) and specific methane production (0.22 to 0.29 Lmethane g CODconsumed). Finally, it can be concluded that different amounts of limestone rocks had no influence on the treatment process in the two studied reactors. Thus, we recommend the use of fewer amount of them since there is a greater useful volume in the reactor. However, the release of calcium and magnesium ions in both reactors assured an alkalinity supply / A água residuária de fecularia é o efluente resultante do processamento da mandioca para extração de fécula e possui alto potencial poluidor devido à elevada concentração de matéria orgânica. O tratamento via biodigestão anaeróbia, além de remover matéria orgânica, viabiliza a produção de biogás e de biofertilizante. No entanto, a eficiência do sistema anaeróbio requer controle da alcalinidade a fim de manter o pH em níveis adequados para a atividade metanogênica. O monitoramento da alcalinidade se faz necessário porque a água residuária de fecularia possui elevado potencial de acidificação, em virtude da presença de altas concentrações de açúcares de rápida fermentação. Essa característica pode ser responsável por elevar os níveis de acidez a ponto de causar problemas à metanogênese. Alguns produtos químicos podem ser empregados nos biodigestores a fim de fornecer alcalinidade ao meio anaeróbio. No entanto, alguns deles podem causar problemas à biodigestão ou aos biodigestores. Assim, com o intuito de evitar esses problemas, o objetivo deste trabalho foi testar os efeitos de diferentes quantidades de pedras de calcário dolomítico sobre o sistema de tratamento anaeróbio de água residuária de fecularia. Foram utilizados dois reatores metanogênicos horizontais com volumes úteis de 3,38 L. A relação entre a massa de pedras de calcário e o volume útil de reator foi de 1:2 no reator A e de 1:4 no reator B. As pedras de calcário, padronizadas de modo a terem entre 9,5 e 11,2 mm de diâmetro, foram dispostas na porção inicial dos reatores, por onde ocorria a entrada da água residuária. Após o período de estabilização dos sistemas de tratamento, foram aplicadas, consecutivamente, seis cargas orgânicas volumétricas (2,30; 3,01; 4,31; 5,69; 7,71 e 8,54 g DQO L-1 d-1), com os respectivos tempos de detenção hidráulica (4,02; 3,07; 2,05; 1,69; 1,69 e 1,13 dias). Observou-se, a cada aumento de carga orgânica volumétrica, que ambos os reatores requeriam o mesmo período para estabilização. Os resultados estatísticos dos parâmetros estudados (pH, alcalinidade parcial, alcalinidade intermediária, alcalinidade total, acidez volátil, relação AV/AT, relação AI/AP, cálcio, magnésio, ácidos orgânicos voláteis, demanda química de oxigênio, série de sólidos totais, biogás, metano, nitrogênio, fósforo, potássio, cobre, zinco, níquel, ferro e manganês) apontaram que ocorreram diferenças significativas entre os dois reatores (quanto às proporções de pedras de calcário testadas) somente em relação ao Mg2+ e aos ST. No entanto, ocorreram diferenças significativas entre as cargas orgânicas aplicadas em cada reator em relação aos parâmetros AP, AT, AV, AV/AT, Ca2+, Mg2+, remoção de DQO total, remoção de DQO filtrada, ST, STF, STV, produção de biogás, produção de metano e produção específica de metano. Essas diferenças indicam que os melhores resultados quanto aos principais parâmetros de monitoramento do sistema anaeróbio ocorreram nos tratamentos 2,30, 3,01 e 4,31 g DQO L-1 d-1, com valores de pH acima de 8,0; elevadas concentrações de alcalinidade devida aos bicarbonatos e alcalinidade total (acima de 1500 mg CaCO3 L-1), coincidindo com as maiores concentrações de íons magnésio nos efluentes dos reatores (67,28 a 114,90 mg L-1); remoções de DQO acima de 90%; porcentagens de metano no biogás entre 73 e 76%; maiores médias de produção específica de biogás (0,31 a 0,49 Lbiogás g DQOconsumida) e de produção específica de metano (0,22 a 0,29 Lmetano g DQOconsumida). Conclui-se, portanto, que as diferentes quantidades de pedras de calcário não tiveram influência sobre o processo de tratamento nos dois reatores. Desta forma, recomenda-se o emprego da menor quantidade de pedras de calcário para que haja maior volume útil no reator. Contudo, a liberação de íons cálcio e magnésio em ambos os reatores garantiu o fornecimento de alcalinidade ao sistema anaeróbio para a rápida estabilização a cada aumento de carga orgânica volumétrica. Palavras-chave: alcalinidade, biogás, cálcio, magnésio

Made available in DSpace on 2017-05-12T14:47:24Z (GMT). No. of bitstreams: 1 Adriana_ Neres de Lima Model.pdf: 1114285 bytes, checksum: 5ac5451e63a53706eccc865aabd911c5 (MD5) Previous issue date: 2016-02-16 / Nitrification associated to autotrophic denitrification, up from an elemental sulfur as an electron donor, can be an adequate option during the post-treatment of anaerobic effluent, which contains ammoniacal nitrogen that should be nitrified, and whose low carbon concentrations (C/N<5) make heterotrophic denitrification difficult. Due to the alkalinity consumption in both processes, lime materials can be applied as alkalizing to ensure the nitrogen removal efficiencies. Therefore, based on this finding, this research has proposed nitrification application followed by autotrophic denitrification in a single reactor containing elemental sulfur and dolomitic limestone to remove nitrogen from an anaerobic effluent from a cold storage from poultry industry. Thus, this study was divided into three steps due to some gaps in literature on the application of autotrophic denitrification up from elemental sulfur in real effluents. In the first step, the performance of autotrophic denitrification was evaluated in four anoxic fixed-bed reactors of elemental sulfur and dolomitic lime at 4:0, 3:1, 1:1 and 1:3 ratios. The reactors were submitted to constant nitrogen feed load (0.114 kg N m³ -1 d-1) under five initial alkalinity conditions (1,000, 800, 600, 400 and 200 mg CaCO3 L-1). The reactors showed similar behavior under those five evaluated experimental conditions. The greatest denitrification efficiencies (from 84.8 to 94.9%) were observed in the first three conditions, whose denitrification rate was 0.102 ± 0.002 kg NOx m³ -1 d-1 and apparent consumption of alkalinity superior to 244.8 mg CaCO3 L-1. Denitrification efficiencies tended to decrease due to the decrease in the initial concentration of alkalinity up from the third experimental condition (600 mg CaCO3 L-1) due to an excessive consumption and inadequate increase of alkalinity (< 180 mg CaCO3 L-1) from dolomitic limestone. During the second step, the anoxic reactor with bed composition (1: 3 ratio), whose initial alkalinity condition was 600 mg CaCO3 L-1, operated at 14, 10 and 6 h HRT. The reactor showed denitrification efficiencies of 94.4 ± 2.0; 94.9 ± 2; 71.1 ± 7.8% as well as denitrification rates of 0.115 ± 0.007; 0.164 ± 0.007 and 0.217 ± 0.025 kg NOx m³ -1 d-1 for HDT of 14, 10 and 6 hours, respectively. At the sixth hour-HRT, the applied overload and limited mass transfer may have contributed to performance decrease into the reactor due to the accumulation of gases in the bed. The third step approached about feeding strategies with mixing ammonified as well as nitrified one in different rates 1:3 (E1), 1:1 (E2) and 3:1 (E3) in anoxic-aerobic reactor of fixed bed with elemental sulfur: dolomitic limestone 1: 3, under 1,000 mg CaCO3 L-1 initial condition of alkalinity. The reactor presented some efficiencies of ammoniacal and total nitrogen removal of 67.3 ± 6.4 and 64.2 ± 6.3% for E1 condition, 63.4 ± 6.4 and 53.1 ± 7.1% for E2 and 14.2 ± 4.4 and 33.8 ± 1.7% for E3. The generation of hydrogen sulfide mainly from sulfur imbalance effect in anoxic compartment may have contributed to a partial inhibition of nitrifying bacteria. The difficulty in keeping the nitrification process was characterized as a limiting factor during nitrogen removal. Low total nitrogen removal efficiencies have implied that nitrification followed by autotrophic denitrification from elemental sulfur in a single reactor was inadequate to remove nitrogenous compounds of anaerobic effluent from a cold storage from poultry industry / A nitrificação acoplada à desnitrificação autotrófica, a partir do enxofre elementar como doador de elétrons, pode ser uma opção adequada no pós-tratamento de efluentes anaeróbios, os quais contêm nitrogênio amoniacal que deve ser nitrificado, cujas baixas concentrações de carbono (C/N<5) dificultam a desnitrificação heterotrófica. Devido ao consumo de alcalinidade nos dois processos, materiais calcários podem ser utilizados como alcalinizantes para garantir as eficiências de remoção do nitrogênio. Com base nessa constatação, esta pesquisa propôs a aplicação da nitrificação seguida da desnitrificação autotrófica em único reator contendo enxofre elementar e calcário dolomítico na remoção de nitrogênio de efluente anaeróbio proveniente de frigorífico avícola. Devido às lacunas presentes na literatura sobre a aplicação da desnitrificação autotrófica a partir do enxofre elementar em efluentes reais, esse estudo foi dividido em três etapas. Na primeira etapa, avaliou-se o desempenho da desnitrificação autotrófica em quatro reatores anóxicos de leito fixo de enxofre elementar e calcário dolomítico nas proporções de 4:0, 3:1, 1:1 e 1:3. Os reatores foram submetidos à alimentação de carga nitrogenada constante de 0,114 kg N m³ -1 d-1 em cinco condições de alcalinidade inicial (1000, 800, 600, 400 e 200 mg CaCO3 L-1). Os reatores apresentaram comportamento semelhante nas cinco condições experimentais avaliadas. As maiores eficiências de desnitrificação (entre 84,8 e 94,9%) foram observadas nas três primeiras condições, com taxa de desnitrificação de 0,102±0,002 kg NOx m³ -1 d-1 e consumo aparente de alcalinidade superior a 244,8 mg CaCO3 L-1. As eficiências de desnitrificação tenderam a diminuir em função do decréscimo da alcalinidade inicial a partir da terceira condição experimental (600 mg CaCO3 L-1) devido ao consumo excessivo e ao incremento insuficiente de alcalinidade (<180 mg CaCO3 L-1) a partir do calcário dolomítico. Na segunda etapa, o reator anóxico com composição de leito na relação de 1:3, em condição inicial de alcalinidade de 600 mg CaCO3 L-1, foi operado em TDH de 14, 10 e 6 horas. O reator apresentou eficiências de desnitrificação de 94,4±2,0 e 94,9±2 e 71,1±7,8% e taxas de desnitrificação de 0,115±0,007, 0,164±0,007 e 0,217±0,025 kg NOx m³ -1 d-1 para os TDH de 14, 10 e 6 horas, respectivamente. No TDH de 6 horas, a sobrecarga aplicada e a limitada transferência de massa, devido ao acúmulo de gases no leito, podem ter contribuído para diminuição do desempenho do reator. A terceira etapa abordou estratégias de alimentação com mistura de efluentes amonificado e nitrificado em diferentes proporções de 1:3 (E1), 1:1 (E2) e 3:1 (E3) em reator anóxico-aeróbio de leito fixo de enxofre elementar: calcário dolomítico de 1:3 em condição inicial de alcalinidade de 1000mg CaCO3L-1. O reator apresentou eficiências de remoção de nitrogênio amoniacal e total de 67,3±6,4 e 64,2±6,3% para a condição E1, 63,4±6,4 e 53,1±7,1% para E2 e 14,2±4 e 33,8±1,7% para E3. A geração de sulfeto de hidrogênio a partir, principalmente, do efeito de desproporção do enxofre no compartimento anóxico, pode ter contribuído para a inibição parcial das bactérias nitrificantes. A dificuldade em manter o processo de nitrificação foi caraterizada como fator limitante na remoção de nitrogênio. As baixas eficiências de remoção de nitrogênio total indicaram que a nitrificação seguida da desnitrificação autotrófica, a partir do enxofre elementar em único reator, não foi adequada para remover compostos nitrogenados de efluente anaeróbio de frigorífico avícola

Made available in DSpace on 2017-05-12T14:47:24Z (GMT). No. of bitstreams: 1 Denise_ Palma.pdf: 3977847 bytes, checksum: f1b9e703a33e6b3a240867b86778aaa2 (MD5) Previous issue date: 2016-02-17 / The wastewater of cassava industry is a resultant effluent from the processing of cassava starch extraction and has a high pollution potential due to its high organic load concentration. Its treatment via anaerobic digestion, in addition to removing organic matter, enables biogas and biofertilizer production. However, the anaerobic system efficiency requires control of alkalinity to keep appropriate levels of pH for methanogenic activity. Alkalinity monitoring is required because its wastewater from starch manufacturer has high potential for acidification, due to the presence of high concentrations of fast fermentation of sugars. This feature can be responsible for increasing acidity levels and can cause problems for methanogenesis. Some chemicals may be applied in digesters in order to provide alkalinity to the anaerobic environment. However, some of them cause problems for digestion or digesters. Thus, in order to avoid these problems, this study tested the effects of different amounts of dolomitic limestone on an anaerobic treatment system of wastewater from cassava industry. Two horizontal-methanogenic reactors with a useful 3.38-liter volume were studied. The relation between mass of dolomitic limestone and working volume was 1:2 in the reactor A and 1:4 in reactor B. The limestone were standardized so that they had diameters varying from 9.5 to 11.2 mm. They were arranged in the initial portion of the reactors, where wastewater came through. After the stabilization period of treatment systems six volumetric organic loads were consecutively applied (2.30; 3.01; 4.31; 5.69; 7.71 and 8.54 gCOD.L-1.d -1), with their respective hydraulic retention times (4.02; 3.07; 2.05; 1.69; 1.69 and 1.13 days). It was observed, for each increase of volumetric organic load that both reactors required the same period for stabilization. The statistical results of the studied parameters (pH, partial alkalinity, intermediate alkalinity, total alkalinity, volatile acidity, ratio VA/TA, ratio IA/PA, calcium, magnesium, volatile organic acids, chemical oxygen demand, number of total solids, biogas and methane, nitrogen, phosphorus, potassium, copper, zinc, nickel, iron and manganese) showed that there were significant differences between the two reactors (based on ratios of the tested limestone) only in relation to Mg2+ and TS. However, there were significant differences between the organic loads applied in each reactor in relation to parameters such as PA, TA, VA, VA/TA, Ca2+, Mg2+, removal of total COD, removal of filtered COD, TS, TFS, TVS, biogas production, methane production, and specific methane production. These differences indicate that the best results regarding the main monitoring parameters of an anaerobic system occurred in treatments 2.30, 3.01 and 4.31 g COD L-1 d-1, with pH values above 8.0; higher concentrations of alkalinity due to bicarbonate and total alkalinity (above 1500 mg CaCO3 L-1). These data closely matched to the highest concentration of magnesium ions in the effluent of reactors (67.28 to 114.90 mg L-1); COD removals were above 90%; methane percentages in biogas varied from 73 to 76%; the highest averages of specific production of biogas were from 0.31 to 0.49 Lbiogas g CODconsumed) and specific methane production (0.22 to 0.29 Lmethane g CODconsumed). Finally, it can be concluded that different amounts of limestone rocks had no influence on the treatment process in the two studied reactors. Thus, we recommend the use of fewer amount of them since there is a greater useful volume in the reactor. However, the release of calcium and magnesium ions in both reactors assured an alkalinity supply / A água residuária de fecularia é o efluente resultante do processamento da mandioca para extração de fécula e possui alto potencial poluidor devido à elevada concentração de matéria orgânica. O tratamento via biodigestão anaeróbia, além de remover matéria orgânica, viabiliza a produção de biogás e de biofertilizante. No entanto, a eficiência do sistema anaeróbio requer controle da alcalinidade a fim de manter o pH em níveis adequados para a atividade metanogênica. O monitoramento da alcalinidade se faz necessário porque a água residuária de fecularia possui elevado potencial de acidificação, em virtude da presença de altas concentrações de açúcares de rápida fermentação. Essa característica pode ser responsável por elevar os níveis de acidez a ponto de causar problemas à metanogênese. Alguns produtos químicos podem ser empregados nos biodigestores a fim de fornecer alcalinidade ao meio anaeróbio. No entanto, alguns deles podem causar problemas à biodigestão ou aos biodigestores. Assim, com o intuito de evitar esses problemas, o objetivo deste trabalho foi testar os efeitos de diferentes quantidades de pedras de calcário dolomítico sobre o sistema de tratamento anaeróbio de água residuária de fecularia. Foram utilizados dois reatores metanogênicos horizontais com volumes úteis de 3,38 L. A relação entre a massa de pedras de calcário e o volume útil de reator foi de 1:2 no reator A e de 1:4 no reator B. As pedras de calcário, padronizadas de modo a terem entre 9,5 e 11,2 mm de diâmetro, foram dispostas na porção inicial dos reatores, por onde ocorria a entrada da água residuária. Após o período de estabilização dos sistemas de tratamento, foram aplicadas, consecutivamente, seis cargas orgânicas volumétricas (2,30; 3,01; 4,31; 5,69; 7,71 e 8,54 g DQO L-1 d-1), com os respectivos tempos de detenção hidráulica (4,02; 3,07; 2,05; 1,69; 1,69 e 1,13 dias). Observou-se, a cada aumento de carga orgânica volumétrica, que ambos os reatores requeriam o mesmo período para estabilização. Os resultados estatísticos dos parâmetros estudados (pH, alcalinidade parcial, alcalinidade intermediária, alcalinidade total, acidez volátil, relação AV/AT, relação AI/AP, cálcio, magnésio, ácidos orgânicos voláteis, demanda química de oxigênio, série de sólidos totais, biogás, metano, nitrogênio, fósforo, potássio, cobre, zinco, níquel, ferro e manganês) apontaram que ocorreram diferenças significativas entre os dois reatores (quanto às proporções de pedras de calcário testadas) somente em relação ao Mg2+ e aos ST. No entanto, ocorreram diferenças significativas entre as cargas orgânicas aplicadas em cada reator em relação aos parâmetros AP, AT, AV, AV/AT, Ca2+, Mg2+, remoção de DQO total, remoção de DQO filtrada, ST, STF, STV, produção de biogás, produção de metano e produção específica de metano. Essas diferenças indicam que os melhores resultados quanto aos principais parâmetros de monitoramento do sistema anaeróbio ocorreram nos tratamentos 2,30, 3,01 e 4,31 g DQO L-1 d-1, com valores de pH acima de 8,0; elevadas concentrações de alcalinidade devida aos bicarbonatos e alcalinidade total (acima de 1500 mg CaCO3 L-1), coincidindo com as maiores concentrações de íons magnésio nos efluentes dos reatores (67,28 a 114,90 mg L-1); remoções de DQO acima de 90%; porcentagens de metano no biogás entre 73 e 76%; maiores médias de produção específica de biogás (0,31 a 0,49 Lbiogás g DQOconsumida) e de produção específica de metano (0,22 a 0,29 Lmetano g DQOconsumida). Conclui-se, portanto, que as diferentes quantidades de pedras de calcário não tiveram influência sobre o processo de tratamento nos dois reatores. Desta forma, recomenda-se o emprego da menor quantidade de pedras de calcário para que haja maior volume útil no reator. Contudo, a liberação de íons cálcio e magnésio em ambos os reatores garantiu o fornecimento de alcalinidade ao sistema anaeróbio para a rápida estabilização a cada aumento de carga orgânica volumétrica. Palavras-chave: alcalinidade, biogás, cálcio, magnésio

Revegetation of bauxite residue is hampered by a lack of understanding of the limitations imposed on plant growth in highly saline and alkaline growth mediums. In this study, several of these growth limiting factors were investigated. The toxicity of the hydroxyl ion (OH-) was examined using a solution culture system developed to allow studies at high pH without nutritional limitations. Also using this solution culture system, the effect of the high Na and Mg concentrations of bauxite residue on the Ca nutrition of plants was investigated. As the toxicity of Al at high pH is not known, a study was conducted to examine the rhizotoxicity of aluminate (Al(OH)4-) and polycationic Al at high pH. The ability of plant roots to reduce rhizosphere pH in bauxite residue was also considered. A novel gypsum application method was assessed for its efficiency at improving the Ca status of bauxite residue. Manual adjustment, ion exchange resins and automated titration were examined for their suitability for nutrient solution pH control in alkaline conditions. For short-term studies, it was found that a solution without supply of Cu, Fe, Mn and Zn, and aerated with CO2 depleted air, greatly reduced nutrient precipitation at high pH, thus eliminating nutritional differences between treatments. Manual pH adjustment and the use of ion exchange resins as pH buffers were unsuitable methods of pH control. In contrast, pH control by automated titration had little effect on solution composition while maintaining constant pH. The solution culture system was used to examine OH- toxicity in mungbeans (Vigna radiata (L.) Wilczek cv. Emerald), with root length reduced at a bulk solution pH of 8.5 and greater. The effect of Ca activity ratio (CAR) and pH on Ca uptake by mungbeans and Rhodes grass (Chloris gayana cv. Pioneer) in Na dominated solution cultures and in soil was investigated. Changes in pH in the alkaline range were shown to have no effect on the critical CAR of 0.024 (corresponding to 90 % relative root length) for mungbeans grown in solution culture. Results from soil grown mungbeans confirmed those from solution culture, with a critical CAR of 0.025. A critical CAR of 0.034 was also established for soil grown Rhodes grass. However, using dilute nutrient solutions dominated by Mg at pH 9.0, root growth was found to be more limited than had been observed for Na solutions, with growth reduced beneath a critical CAR of 0.050. Using a CAR equation modified with plasma membrane binding constants (to incorporate the differing antagonistic effects of Mg and Na), new critical CAR values were calculated for Na (0.56) and Mg (0.44) dominated solutions. This modified CAR equation permits the calculation of CAR irrespective of the dominant salt present. Solubilities of various gypsum sources and size fractions in seawater were studied to investigate the effectiveness of gypsum addition to the residue sand pipeline, rather than as a direct field application. The dissolution rate constant varied with gypsum source (analytical grade (AR) > phosphogypsum (PG) > mined gypsum (MG)) due to reactivity and surface area differences, generally reaching saturation within 15 s (AR) to 30 min (MG > 2.0). The ability of bauxite residue to remove Ca from solution (due to cation exchange and precipitation) was also examined; the quantity of the total solution Ca adsorbed was found to be small (5 %). These low rates of solution Ca adsorption, comparatively rapid dissolution rates, and long pumping times (20 min), preclude the application of gypsum to the residue sand/seawater slurry as a method for residue amelioration. Dilute, alkaline (pH 9.5) nutrient solutions were used to investigate the effects of aluminate (Al(OH)4-) on mungbean root growth. Although root growth in Al(OH)4- solutions was slightly limited, the symptoms associated with this growth reduction were observed to be similar to those caused by the Al13 polycation at concentrations lower than that which can be detected. Also, when roots displaying these symptoms were transferred to fresh Al(OH)4- solutions, no root tip lesions were observed, and root hair growth on the lateral roots improved. Thus, Al(OH)4- is considered to be non-toxic, with the observed reduction in root growth in solutions containing Al(OH)4- due to the gradual formation of toxic Al13 in the bulk nutrient solution resulting from the acidification of the alkaline nutrient solution by the plant roots. The effect of Mn deficiency in Rhodes grass and of legume inoculation in lucerne (Medicago sativa L. cv. Hunter River), on the rhizosphere pH of plants grown in highly alkaline bauxite residue was investigated. In response to Mn deficiency in residue sand, Rhodes grass was observed to increase acidification of its rhizosphere (being up to 1.22 pH units lower than the bulk soil). Due to its ability to fix atmospheric N2 rather than relying on soil N (NO3-) reserves, inoculated lucerne (1.75 pH unit decrease) was also found to acidify its rhizosphere to a greater extent than non-inoculated lucerne (1.16 pH unit decrease).

Revegetation of bauxite residue is hampered by a lack of understanding of the limitations imposed on plant growth in highly saline and alkaline growth mediums. In this study, several of these growth limiting factors were investigated. The toxicity of the hydroxyl ion (OH-) was examined using a solution culture system developed to allow studies at high pH without nutritional limitations. Also using this solution culture system, the effect of the high Na and Mg concentrations of bauxite residue on the Ca nutrition of plants was investigated. As the toxicity of Al at high pH is not known, a study was conducted to examine the rhizotoxicity of aluminate (Al(OH)4-) and polycationic Al at high pH. The ability of plant roots to reduce rhizosphere pH in bauxite residue was also considered. A novel gypsum application method was assessed for its efficiency at improving the Ca status of bauxite residue. Manual adjustment, ion exchange resins and automated titration were examined for their suitability for nutrient solution pH control in alkaline conditions. For short-term studies, it was found that a solution without supply of Cu, Fe, Mn and Zn, and aerated with CO2 depleted air, greatly reduced nutrient precipitation at high pH, thus eliminating nutritional differences between treatments. Manual pH adjustment and the use of ion exchange resins as pH buffers were unsuitable methods of pH control. In contrast, pH control by automated titration had little effect on solution composition while maintaining constant pH. The solution culture system was used to examine OH- toxicity in mungbeans (Vigna radiata (L.) Wilczek cv. Emerald), with root length reduced at a bulk solution pH of 8.5 and greater. The effect of Ca activity ratio (CAR) and pH on Ca uptake by mungbeans and Rhodes grass (Chloris gayana cv. Pioneer) in Na dominated solution cultures and in soil was investigated. Changes in pH in the alkaline range were shown to have no effect on the critical CAR of 0.024 (corresponding to 90 % relative root length) for mungbeans grown in solution culture. Results from soil grown mungbeans confirmed those from solution culture, with a critical CAR of 0.025. A critical CAR of 0.034 was also established for soil grown Rhodes grass. However, using dilute nutrient solutions dominated by Mg at pH 9.0, root growth was found to be more limited than had been observed for Na solutions, with growth reduced beneath a critical CAR of 0.050. Using a CAR equation modified with plasma membrane binding constants (to incorporate the differing antagonistic effects of Mg and Na), new critical CAR values were calculated for Na (0.56) and Mg (0.44) dominated solutions. This modified CAR equation permits the calculation of CAR irrespective of the dominant salt present. Solubilities of various gypsum sources and size fractions in seawater were studied to investigate the effectiveness of gypsum addition to the residue sand pipeline, rather than as a direct field application. The dissolution rate constant varied with gypsum source (analytical grade (AR) > phosphogypsum (PG) > mined gypsum (MG)) due to reactivity and surface area differences, generally reaching saturation within 15 s (AR) to 30 min (MG > 2.0). The ability of bauxite residue to remove Ca from solution (due to cation exchange and precipitation) was also examined; the quantity of the total solution Ca adsorbed was found to be small (5 %). These low rates of solution Ca adsorption, comparatively rapid dissolution rates, and long pumping times (20 min), preclude the application of gypsum to the residue sand/seawater slurry as a method for residue amelioration. Dilute, alkaline (pH 9.5) nutrient solutions were used to investigate the effects of aluminate (Al(OH)4-) on mungbean root growth. Although root growth in Al(OH)4- solutions was slightly limited, the symptoms associated with this growth reduction were observed to be similar to those caused by the Al13 polycation at concentrations lower than that which can be detected. Also, when roots displaying these symptoms were transferred to fresh Al(OH)4- solutions, no root tip lesions were observed, and root hair growth on the lateral roots improved. Thus, Al(OH)4- is considered to be non-toxic, with the observed reduction in root growth in solutions containing Al(OH)4- due to the gradual formation of toxic Al13 in the bulk nutrient solution resulting from the acidification of the alkaline nutrient solution by the plant roots. The effect of Mn deficiency in Rhodes grass and of legume inoculation in lucerne (Medicago sativa L. cv. Hunter River), on the rhizosphere pH of plants grown in highly alkaline bauxite residue was investigated. In response to Mn deficiency in residue sand, Rhodes grass was observed to increase acidification of its rhizosphere (being up to 1.22 pH units lower than the bulk soil). Due to its ability to fix atmospheric N2 rather than relying on soil N (NO3-) reserves, inoculated lucerne (1.75 pH unit decrease) was also found to acidify its rhizosphere to a greater extent than non-inoculated lucerne (1.16 pH unit decrease).

The flux of CO2 between the ocean and the atmosphere is an important measure in determining local, global, and regional, as well as short term and long term carbon budgets. In this study, air-sea CO2 fluxes measured using a floating chamber were used to examine the spatial and temporal variability of CO2 fluxes in Florida Bay. Measurements of dissolved inorganic carbon and total alkalinity obtained concurrently with chamber measurements of CO2 flux allowed calculation of ΔpCO2 from flux measurements obtained at zero wind velocity. Floating chamber measurements of ΔpCO2 were subsequently coupled with wind speed data to provide a simple yet reliable means of predicting absolute flux values. Florida Bay is a marine-dominated, sub-tropical estuary located at the southern tip of the Florida peninsula. Spatial variability within the bay reveals four distinct regions that appear to be affected by a variety of physical, chemical and biological processes. In the eastern part of the bay, the waters tend to be oversaturated with respect to CO2, likely due to the input of freshwater from Taylor Slough. The central portion of the bay is characterized by a number of extremely shallow semi-isolated basins with limited exchange with the rest of the bay. This area is typically undersaturated with respect to CO2 and provides a sink for atmospheric CO2. Both the northern and southern regions were highly variable both spatially and temporally.

Revegetation of bauxite residue is hampered by a lack of understanding of the limitations imposed on plant growth in highly saline and alkaline growth mediums. In this study, several of these growth limiting factors were investigated. The toxicity of the hydroxyl ion (OH-) was examined using a solution culture system developed to allow studies at high pH without nutritional limitations. Also using this solution culture system, the effect of the high Na and Mg concentrations of bauxite residue on the Ca nutrition of plants was investigated. As the toxicity of Al at high pH is not known, a study was conducted to examine the rhizotoxicity of aluminate (Al(OH)4-) and polycationic Al at high pH. The ability of plant roots to reduce rhizosphere pH in bauxite residue was also considered. A novel gypsum application method was assessed for its efficiency at improving the Ca status of bauxite residue. Manual adjustment, ion exchange resins and automated titration were examined for their suitability for nutrient solution pH control in alkaline conditions. For short-term studies, it was found that a solution without supply of Cu, Fe, Mn and Zn, and aerated with CO2 depleted air, greatly reduced nutrient precipitation at high pH, thus eliminating nutritional differences between treatments. Manual pH adjustment and the use of ion exchange resins as pH buffers were unsuitable methods of pH control. In contrast, pH control by automated titration had little effect on solution composition while maintaining constant pH. The solution culture system was used to examine OH- toxicity in mungbeans (Vigna radiata (L.) Wilczek cv. Emerald), with root length reduced at a bulk solution pH of 8.5 and greater. The effect of Ca activity ratio (CAR) and pH on Ca uptake by mungbeans and Rhodes grass (Chloris gayana cv. Pioneer) in Na dominated solution cultures and in soil was investigated. Changes in pH in the alkaline range were shown to have no effect on the critical CAR of 0.024 (corresponding to 90 % relative root length) for mungbeans grown in solution culture. Results from soil grown mungbeans confirmed those from solution culture, with a critical CAR of 0.025. A critical CAR of 0.034 was also established for soil grown Rhodes grass. However, using dilute nutrient solutions dominated by Mg at pH 9.0, root growth was found to be more limited than had been observed for Na solutions, with growth reduced beneath a critical CAR of 0.050. Using a CAR equation modified with plasma membrane binding constants (to incorporate the differing antagonistic effects of Mg and Na), new critical CAR values were calculated for Na (0.56) and Mg (0.44) dominated solutions. This modified CAR equation permits the calculation of CAR irrespective of the dominant salt present. Solubilities of various gypsum sources and size fractions in seawater were studied to investigate the effectiveness of gypsum addition to the residue sand pipeline, rather than as a direct field application. The dissolution rate constant varied with gypsum source (analytical grade (AR) > phosphogypsum (PG) > mined gypsum (MG)) due to reactivity and surface area differences, generally reaching saturation within 15 s (AR) to 30 min (MG > 2.0). The ability of bauxite residue to remove Ca from solution (due to cation exchange and precipitation) was also examined; the quantity of the total solution Ca adsorbed was found to be small (5 %). These low rates of solution Ca adsorption, comparatively rapid dissolution rates, and long pumping times (20 min), preclude the application of gypsum to the residue sand/seawater slurry as a method for residue amelioration. Dilute, alkaline (pH 9.5) nutrient solutions were used to investigate the effects of aluminate (Al(OH)4-) on mungbean root growth. Although root growth in Al(OH)4- solutions was slightly limited, the symptoms associated with this growth reduction were observed to be similar to those caused by the Al13 polycation at concentrations lower than that which can be detected. Also, when roots displaying these symptoms were transferred to fresh Al(OH)4- solutions, no root tip lesions were observed, and root hair growth on the lateral roots improved. Thus, Al(OH)4- is considered to be non-toxic, with the observed reduction in root growth in solutions containing Al(OH)4- due to the gradual formation of toxic Al13 in the bulk nutrient solution resulting from the acidification of the alkaline nutrient solution by the plant roots. The effect of Mn deficiency in Rhodes grass and of legume inoculation in lucerne (Medicago sativa L. cv. Hunter River), on the rhizosphere pH of plants grown in highly alkaline bauxite residue was investigated. In response to Mn deficiency in residue sand, Rhodes grass was observed to increase acidification of its rhizosphere (being up to 1.22 pH units lower than the bulk soil). Due to its ability to fix atmospheric N2 rather than relying on soil N (NO3-) reserves, inoculated lucerne (1.75 pH unit decrease) was also found to acidify its rhizosphere to a greater extent than non-inoculated lucerne (1.16 pH unit decrease).

Revegetation of bauxite residue is hampered by a lack of understanding of the limitations imposed on plant growth in highly saline and alkaline growth mediums. In this study, several of these growth limiting factors were investigated. The toxicity of the hydroxyl ion (OH-) was examined using a solution culture system developed to allow studies at high pH without nutritional limitations. Also using this solution culture system, the effect of the high Na and Mg concentrations of bauxite residue on the Ca nutrition of plants was investigated. As the toxicity of Al at high pH is not known, a study was conducted to examine the rhizotoxicity of aluminate (Al(OH)4-) and polycationic Al at high pH. The ability of plant roots to reduce rhizosphere pH in bauxite residue was also considered. A novel gypsum application method was assessed for its efficiency at improving the Ca status of bauxite residue. Manual adjustment, ion exchange resins and automated titration were examined for their suitability for nutrient solution pH control in alkaline conditions. For short-term studies, it was found that a solution without supply of Cu, Fe, Mn and Zn, and aerated with CO2 depleted air, greatly reduced nutrient precipitation at high pH, thus eliminating nutritional differences between treatments. Manual pH adjustment and the use of ion exchange resins as pH buffers were unsuitable methods of pH control. In contrast, pH control by automated titration had little effect on solution composition while maintaining constant pH. The solution culture system was used to examine OH- toxicity in mungbeans (Vigna radiata (L.) Wilczek cv. Emerald), with root length reduced at a bulk solution pH of 8.5 and greater. The effect of Ca activity ratio (CAR) and pH on Ca uptake by mungbeans and Rhodes grass (Chloris gayana cv. Pioneer) in Na dominated solution cultures and in soil was investigated. Changes in pH in the alkaline range were shown to have no effect on the critical CAR of 0.024 (corresponding to 90 % relative root length) for mungbeans grown in solution culture. Results from soil grown mungbeans confirmed those from solution culture, with a critical CAR of 0.025. A critical CAR of 0.034 was also established for soil grown Rhodes grass. However, using dilute nutrient solutions dominated by Mg at pH 9.0, root growth was found to be more limited than had been observed for Na solutions, with growth reduced beneath a critical CAR of 0.050. Using a CAR equation modified with plasma membrane binding constants (to incorporate the differing antagonistic effects of Mg and Na), new critical CAR values were calculated for Na (0.56) and Mg (0.44) dominated solutions. This modified CAR equation permits the calculation of CAR irrespective of the dominant salt present. Solubilities of various gypsum sources and size fractions in seawater were studied to investigate the effectiveness of gypsum addition to the residue sand pipeline, rather than as a direct field application. The dissolution rate constant varied with gypsum source (analytical grade (AR) > phosphogypsum (PG) > mined gypsum (MG)) due to reactivity and surface area differences, generally reaching saturation within 15 s (AR) to 30 min (MG > 2.0). The ability of bauxite residue to remove Ca from solution (due to cation exchange and precipitation) was also examined; the quantity of the total solution Ca adsorbed was found to be small (5 %). These low rates of solution Ca adsorption, comparatively rapid dissolution rates, and long pumping times (20 min), preclude the application of gypsum to the residue sand/seawater slurry as a method for residue amelioration. Dilute, alkaline (pH 9.5) nutrient solutions were used to investigate the effects of aluminate (Al(OH)4-) on mungbean root growth. Although root growth in Al(OH)4- solutions was slightly limited, the symptoms associated with this growth reduction were observed to be similar to those caused by the Al13 polycation at concentrations lower than that which can be detected. Also, when roots displaying these symptoms were transferred to fresh Al(OH)4- solutions, no root tip lesions were observed, and root hair growth on the lateral roots improved. Thus, Al(OH)4- is considered to be non-toxic, with the observed reduction in root growth in solutions containing Al(OH)4- due to the gradual formation of toxic Al13 in the bulk nutrient solution resulting from the acidification of the alkaline nutrient solution by the plant roots. The effect of Mn deficiency in Rhodes grass and of legume inoculation in lucerne (Medicago sativa L. cv. Hunter River), on the rhizosphere pH of plants grown in highly alkaline bauxite residue was investigated. In response to Mn deficiency in residue sand, Rhodes grass was observed to increase acidification of its rhizosphere (being up to 1.22 pH units lower than the bulk soil). Due to its ability to fix atmospheric N2 rather than relying on soil N (NO3-) reserves, inoculated lucerne (1.75 pH unit decrease) was also found to acidify its rhizosphere to a greater extent than non-inoculated lucerne (1.16 pH unit decrease).

Revegetation of bauxite residue is hampered by a lack of understanding of the limitations imposed on plant growth in highly saline and alkaline growth mediums. In this study, several of these growth limiting factors were investigated. The toxicity of the hydroxyl ion (OH-) was examined using a solution culture system developed to allow studies at high pH without nutritional limitations. Also using this solution culture system, the effect of the high Na and Mg concentrations of bauxite residue on the Ca nutrition of plants was investigated. As the toxicity of Al at high pH is not known, a study was conducted to examine the rhizotoxicity of aluminate (Al(OH)4-) and polycationic Al at high pH. The ability of plant roots to reduce rhizosphere pH in bauxite residue was also considered. A novel gypsum application method was assessed for its efficiency at improving the Ca status of bauxite residue. Manual adjustment, ion exchange resins and automated titration were examined for their suitability for nutrient solution pH control in alkaline conditions. For short-term studies, it was found that a solution without supply of Cu, Fe, Mn and Zn, and aerated with CO2 depleted air, greatly reduced nutrient precipitation at high pH, thus eliminating nutritional differences between treatments. Manual pH adjustment and the use of ion exchange resins as pH buffers were unsuitable methods of pH control. In contrast, pH control by automated titration had little effect on solution composition while maintaining constant pH. The solution culture system was used to examine OH- toxicity in mungbeans (Vigna radiata (L.) Wilczek cv. Emerald), with root length reduced at a bulk solution pH of 8.5 and greater. The effect of Ca activity ratio (CAR) and pH on Ca uptake by mungbeans and Rhodes grass (Chloris gayana cv. Pioneer) in Na dominated solution cultures and in soil was investigated. Changes in pH in the alkaline range were shown to have no effect on the critical CAR of 0.024 (corresponding to 90 % relative root length) for mungbeans grown in solution culture. Results from soil grown mungbeans confirmed those from solution culture, with a critical CAR of 0.025. A critical CAR of 0.034 was also established for soil grown Rhodes grass. However, using dilute nutrient solutions dominated by Mg at pH 9.0, root growth was found to be more limited than had been observed for Na solutions, with growth reduced beneath a critical CAR of 0.050. Using a CAR equation modified with plasma membrane binding constants (to incorporate the differing antagonistic effects of Mg and Na), new critical CAR values were calculated for Na (0.56) and Mg (0.44) dominated solutions. This modified CAR equation permits the calculation of CAR irrespective of the dominant salt present. Solubilities of various gypsum sources and size fractions in seawater were studied to investigate the effectiveness of gypsum addition to the residue sand pipeline, rather than as a direct field application. The dissolution rate constant varied with gypsum source (analytical grade (AR) > phosphogypsum (PG) > mined gypsum (MG)) due to reactivity and surface area differences, generally reaching saturation within 15 s (AR) to 30 min (MG > 2.0). The ability of bauxite residue to remove Ca from solution (due to cation exchange and precipitation) was also examined; the quantity of the total solution Ca adsorbed was found to be small (5 %). These low rates of solution Ca adsorption, comparatively rapid dissolution rates, and long pumping times (20 min), preclude the application of gypsum to the residue sand/seawater slurry as a method for residue amelioration. Dilute, alkaline (pH 9.5) nutrient solutions were used to investigate the effects of aluminate (Al(OH)4-) on mungbean root growth. Although root growth in Al(OH)4- solutions was slightly limited, the symptoms associated with this growth reduction were observed to be similar to those caused by the Al13 polycation at concentrations lower than that which can be detected. Also, when roots displaying these symptoms were transferred to fresh Al(OH)4- solutions, no root tip lesions were observed, and root hair growth on the lateral roots improved. Thus, Al(OH)4- is considered to be non-toxic, with the observed reduction in root growth in solutions containing Al(OH)4- due to the gradual formation of toxic Al13 in the bulk nutrient solution resulting from the acidification of the alkaline nutrient solution by the plant roots. The effect of Mn deficiency in Rhodes grass and of legume inoculation in lucerne (Medicago sativa L. cv. Hunter River), on the rhizosphere pH of plants grown in highly alkaline bauxite residue was investigated. In response to Mn deficiency in residue sand, Rhodes grass was observed to increase acidification of its rhizosphere (being up to 1.22 pH units lower than the bulk soil). Due to its ability to fix atmospheric N2 rather than relying on soil N (NO3-) reserves, inoculated lucerne (1.75 pH unit decrease) was also found to acidify its rhizosphere to a greater extent than non-inoculated lucerne (1.16 pH unit decrease).

Revegetation of bauxite residue is hampered by a lack of understanding of the limitations imposed on plant growth in highly saline and alkaline growth mediums. In this study, several of these growth limiting factors were investigated. The toxicity of the hydroxyl ion (OH-) was examined using a solution culture system developed to allow studies at high pH without nutritional limitations. Also using this solution culture system, the effect of the high Na and Mg concentrations of bauxite residue on the Ca nutrition of plants was investigated. As the toxicity of Al at high pH is not known, a study was conducted to examine the rhizotoxicity of aluminate (Al(OH)4-) and polycationic Al at high pH. The ability of plant roots to reduce rhizosphere pH in bauxite residue was also considered. A novel gypsum application method was assessed for its efficiency at improving the Ca status of bauxite residue. Manual adjustment, ion exchange resins and automated titration were examined for their suitability for nutrient solution pH control in alkaline conditions. For short-term studies, it was found that a solution without supply of Cu, Fe, Mn and Zn, and aerated with CO2 depleted air, greatly reduced nutrient precipitation at high pH, thus eliminating nutritional differences between treatments. Manual pH adjustment and the use of ion exchange resins as pH buffers were unsuitable methods of pH control. In contrast, pH control by automated titration had little effect on solution composition while maintaining constant pH. The solution culture system was used to examine OH- toxicity in mungbeans (Vigna radiata (L.) Wilczek cv. Emerald), with root length reduced at a bulk solution pH of 8.5 and greater. The effect of Ca activity ratio (CAR) and pH on Ca uptake by mungbeans and Rhodes grass (Chloris gayana cv. Pioneer) in Na dominated solution cultures and in soil was investigated. Changes in pH in the alkaline range were shown to have no effect on the critical CAR of 0.024 (corresponding to 90 % relative root length) for mungbeans grown in solution culture. Results from soil grown mungbeans confirmed those from solution culture, with a critical CAR of 0.025. A critical CAR of 0.034 was also established for soil grown Rhodes grass. However, using dilute nutrient solutions dominated by Mg at pH 9.0, root growth was found to be more limited than had been observed for Na solutions, with growth reduced beneath a critical CAR of 0.050. Using a CAR equation modified with plasma membrane binding constants (to incorporate the differing antagonistic effects of Mg and Na), new critical CAR values were calculated for Na (0.56) and Mg (0.44) dominated solutions. This modified CAR equation permits the calculation of CAR irrespective of the dominant salt present. Solubilities of various gypsum sources and size fractions in seawater were studied to investigate the effectiveness of gypsum addition to the residue sand pipeline, rather than as a direct field application. The dissolution rate constant varied with gypsum source (analytical grade (AR) > phosphogypsum (PG) > mined gypsum (MG)) due to reactivity and surface area differences, generally reaching saturation within 15 s (AR) to 30 min (MG > 2.0). The ability of bauxite residue to remove Ca from solution (due to cation exchange and precipitation) was also examined; the quantity of the total solution Ca adsorbed was found to be small (5 %). These low rates of solution Ca adsorption, comparatively rapid dissolution rates, and long pumping times (20 min), preclude the application of gypsum to the residue sand/seawater slurry as a method for residue amelioration. Dilute, alkaline (pH 9.5) nutrient solutions were used to investigate the effects of aluminate (Al(OH)4-) on mungbean root growth. Although root growth in Al(OH)4- solutions was slightly limited, the symptoms associated with this growth reduction were observed to be similar to those caused by the Al13 polycation at concentrations lower than that which can be detected. Also, when roots displaying these symptoms were transferred to fresh Al(OH)4- solutions, no root tip lesions were observed, and root hair growth on the lateral roots improved. Thus, Al(OH)4- is considered to be non-toxic, with the observed reduction in root growth in solutions containing Al(OH)4- due to the gradual formation of toxic Al13 in the bulk nutrient solution resulting from the acidification of the alkaline nutrient solution by the plant roots. The effect of Mn deficiency in Rhodes grass and of legume inoculation in lucerne (Medicago sativa L. cv. Hunter River), on the rhizosphere pH of plants grown in highly alkaline bauxite residue was investigated. In response to Mn deficiency in residue sand, Rhodes grass was observed to increase acidification of its rhizosphere (being up to 1.22 pH units lower than the bulk soil). Due to its ability to fix atmospheric N2 rather than relying on soil N (NO3-) reserves, inoculated lucerne (1.75 pH unit decrease) was also found to acidify its rhizosphere to a greater extent than non-inoculated lucerne (1.16 pH unit decrease).