Microalgae have a variety of commercial applications, the oldest of which include utilisation as a food source and for use in wastewater treatment. These applications, however, are seldom combined due to toxicity concerns, for ethical reasons, and generally the requirement for cultivation of a single algae species for use as a feed supplement. These problems might be negated if a “safer” wastewater such as that from agricultural and/or commercial food production facilities were to be utilised and if a stable algae population can be maintained. In this investigation preliminary studies were carried out using an Integrated Algae Pond System (IAPS) for domestic wastewater treatment to determine the species composition in the associated High Rate Algae Ponds (HRAPs). The effect of different modes of operation, continuous versus batch, on nutrient removal, productivity and species composition was also investigated. Furthermore, indigenous species in the HRAP were isolated and molecularly identified as, Chlorella, Micractinium, Scenedesmus and Pediastrum. Additionally, the effect of the nor amino acid, 2-hydroxy-4-(methylthio)-butanoic acid (HMTBA) and its Cu-chelated derivative, on the growth and biochemical composition of Chlorella, Micractinium, Scenedesmus, Pediastrum and Spirulina was investigated. Species composition in the HRAP was stable under continuous operation with Micractinium dominating > 90% of the algae population. Under batch operation the population dynamic shifted; Chlorella outcompeted Micractinium possibly due to nutrient depletion and selective grazing pressures caused by proliferation of Daphnia. Higher species diversity was observed during batch mode as slower growing algae were able to establish in the HRAP. Nutrient removal efficiency and biomass productivity was higher in continuous mode, however lower nutrient levels were obtained in batch operation. HMTBA did not significantly affect growth rate, however treatment with 10 mg.L-1 resulted in slightly increased growth rate in Micractinium and increased final biomass concentrations in Chlorella, Micractinium and Spirulina (although this was not statistically significant for Micractinium and Spirulina), which are known mixotrophic species. Algae treated with Cu-HMTBA, showed reduced final biomass concentration with 10 mg.L-1, caused by Cu toxicity. Biochemical composition of the algae was species-specific and differed through the growth cycle, with high protein observed during early growth and high carbohydrate during late growth/early stationary phase. Additionally, 0.1 mg.L-1 HMTBA and Cu-HMTBA significantly reduced protein content in Chlorella, Micractinium, Scenedesmus and Pediastrum. In conclusion, operation of the HRAP in continuous culture provided suitable wastewater treatment with high productivity of an ideal species, Micractinium, for use in animal feed supplementation. This species had 40% protein content during growth (higher than the other species tested) and dominated the HRAP at > 90% of the algae population during continuous mode. Addition of HMTBA (> 1 mg.L-1) to algae cultivation systems and those treating wastewater, has the potential to improve productivity and the value of the biomass by enhancing protein content. Overall, the co-utilisation of microalgae for wastewater treatment and the generation of a biomass rich in protein, for incorporation into formulated animal feed supplements, represents a closed ecosystem which conserves nutrients and regenerates a most valuable resource, water.

Le recyclage des résidus organiques (RO) en agriculture pourrait permettre de limiter l’utilisation des ressources minérales de phosphore (P), à condition de déterminer leur efficacité pour fournir du P aux cultures. L’objectif de ce travail était donc d’étudier les mécanismes déterminant l’effet des RO apportés au sol sur la biodisponibilité du P pour la plante (phytodisponibilité). Ce travail a été basé sur cinq essais de terrain à La Réunion, fertilisés sur une décennie avec des fertilisants organiques ou minéraux, et sur des expérimentations d’incubations en conditions contrôlées et de cultures de plantes en pot. Le P inorganique (Pi) et organique (Po) disponible du sol a été déterminé par des extractions (eau, Olsen), la technique des diffusive gradients in thin films (DGT) et la dilution isotopique associée à des membranes échangeuses d’ions. La capacité de sorption en Pi des sols a été évaluée avec des courbes de sorption. Le P phytodisponible a été déterminé en mesurant le P prélevé par la plante. Dans les différents types de sol (andosol, andique cambisol, nitisol et arenosol), l’apport de RO a augmenté le Pi disponible relativement au Po, suggérant que la minéralisation du Po issu des RO n’est pas un facteur limitant la disponibilité du Pi. Les RO ont augmenté le Pi disponible principalement par l’augmentation du pH du sol et par conséquent la diminution de sa capacité de sorption de Pi. Le P phytodisponible a augmenté avec le Pi disponible du sol, mais a diminué avec l’augmentation du pH du sol. Au-delà de la dose de P, l’effet de l’apport de RO à long-terme sur la phytodisponibilité du P semble principalement contrôlé par l’évolution induite du pH du sol. / Application of organic residues (OR) on agricultural soils could reduce the use of mineral phosphorus (P) fertilizers, but this implies to determine the efficiency of OR to meet crop requirements. We thus aimed to study mechanisms determining the effects of OR on P bioavailability to plants (phytoavailability). Our work was based on five field trials with decadal organic or mineral fertilization located in Réunion island, and on incubations and plant growth experiments under controlled conditions. Available inorganic P (Pi) and organic P (Po) was determined using extractions (water, Olsen), the diffusive gradients in thin films technique (DGT) and the isotopic dilution associated to anion exchange membranes (EAEM). Phytoavailable P was determined as the plant P uptake. Soil Pi sorption capacity was determined using sorption curves. For all soil types studied (andosol, andic cambisol, nitisol, and arenosol), RO increased mainly available Pi and had few effects on available Po, which suggests that mineralization of Po applied with RO does not limit Pi availability. Application of RO increased available Pi mainly by increasing soil pH and consequently by decreasing soil Pi sorption capacity. Phytoavailable P increased with soil available Pi, but decreased with increasing soil pH. Our work suggests that except the dose of P applied, effect of RO on P phytoavailability depends mainly on soil pH changes induced.

Orientador: Leandro Cardoso de Morais / Resumo: O Brasil se destaca na produção do ferro e aço, e principalmente na utilização de fontes renováveis como insumos energéticos para sua produção. O biocoque possui potencial para utilização de biomassas como insumos energéticos em alto fornos, em substituição aos tradicionais combustíveis fósseis, carvão e coque, porém, ainda é um material pouco conhecido cientificamente. O objetivo foi encontrar os parâmetros adequados para a produção, em escala laboratorial, do biocoque de casca e serragem da madeira de eucalipto. Também verificar suas principais características térmicas e físico-químicas, antes e após a produção do biocoque. Foi usado a casca e serragem de eucalipto para a produção do biocoque. Os materiais passaram por analises de umidade, analise imediata, analise elementar, poder calorífico, densidades, resistência mecânica, estabilidade dimensional, termogravimetria, microscopia MEV, espectroscopia FTIR e EDS, difratometria de raio-x e análises cinética. O biocoque para ambos os materiais foram prensados com força de 10 toneladas sob 180 °C de temperatura por 10 minutos, apresentando características físico-químicas adequadas para o uso. Os biocoques tiveram caracteristicas físicas adequadas a necessidade de uso com alta resistência mecânica, com aproximadamente 10 MPa para ambos os materiais e durabilidade acima de 99 %. A densidade aparente (1.350 kg.m-3) foi aumentada aproximadamente cinco vezes comparado ao valor inicial para o material particulado. Os materiais apres... (Resumo completo, clicar acesso eletrônico abaixo) / Doutor

El alperujo (AL) es uno de los principales residuos agroindustriales que se generan actualmente en España. Su tratamiento mediante compostaje ha demostrado ser suficientemente viable para su revalorización y utilización agrícola, conduciendo a la producción de composts ricos en materia orgánica humificada de clara naturaleza lignocelulósica, que pueden constituir una excelente materia prima para la producción industrial de abonos orgánicos y órgano-minerales de calidad. En el presente trabajo se ha estudiado a escala pre-industrial la viabilidad del compostaje de AL demostrando que con este proceso se pueden llegar a obtener cerca de 20 categorías de abonos y enmiendas orgánicas comerciales tanto en sus formas sólidas como líquidas de acuerdo con la legislación vigente (Real Decreto 824/2005).

[Truncated abstract] Relationships between the persistence of organic matter added to soil, the dynamics of soil organic carbon (C) and phosphorus (P) were examined in four experiments on lateritic soils of Western Australia. The main objective was to quantify the release of P following organic matter application in soils which have high P adsorbing capacity. Another objective was to confirm that due to its recalcitrant materials, the effect of peat lasted longer in soil than other sources of organic matter in terms of increasing plant-available P fractions. Three experiments were conducted under glasshouse conditions for various lengths of time, with nine- to twelve-month incubations to investigate these hypotheses. As expected, organic matter with lower C:N ratios than peat (lucerne hay) decomposed more rapidly compared with peat, and the most active mineralisation took place within the first three months of incubation. Soil organic-C (extracted by 0.5 M K2SO4) had a significant positive correlation with P extracted with 0.5 M NaHCO pH 8.53. For a higher application rate (120 ton ha-1), peat was better than wheat straw and lucerne hay in increasing extractable bicarbonate-P concentrations in soil, especially at incubation times up to 12 months. Throughout the experiment, peat was associated with a steady increase in all parameters measured. In contrast to peat, nutrient release from lucerne hay and wheat straw was rapid and diminished over time. There was a tendency for organic-C (either in the form of total extractable organic-C or microbial biomass-C) to steadily increase in soil with added peat throughout the experiment. Unlike wheat straw and lucerne hay, extractable organic-C from peat remained in soil and there was less C loss in the form of respiration. Therefore, peat persisted and sequestered C to the soil system for a longer time than the other source of organic matter. Freshly added organic matter was expected to have a greater influence on P transformation from adsorbed forms in lateritic soils than existing soil organic matter. By removing the existing soil organic matter, the effect of freshly applied organic matter can be determine separately from that of the existing soil organic matter for a similar organic-C content. In order to do this, some soil samples were combusted up to 450° C to eliminate inherent soil organic matter. The release of P was greater when organic-C from fresh organic matter was applied to combusted soils than in uncombusted soils that contained the existing soil organic matter. The exception only applied for parameters related to soil micro-organisms such as biomass-C and phosphatase. For such parameters, new soil organic matter did not create conditions favourable for organisms to increase in activity despite the abundance of organic matter available. More non-extractable-P was formed in combusted soils compared to bicarbonate-P and it contributed to more than 50% of total-P. As for the first experiment, peat also showed a constant effect in increasing bicarbonate extractable-P in the soil

Population escalation in the developing world has been associated with increased poverty, food insecurity and environmental degradation. The situation in Rwanda, with 2.82% annual population increase is no exception. The objective of the present study was to investigate an innovative integrated system of sustainable production suitable for resource-poor rural farmers, the Integrated Rabbit–Fish–Rice (IRFR) system. The study was targeted towards contributing to Rwanda government’s goals of eradicating extreme poverty and hunger, enhancing food security as well as abating environmental degradation. Three experiments, were carried out between 2008 and 2010, and designed to fertilise pond water with rabbit droppings and boost phytoplankton production. We also used results from our previous study, conducted in 2005 in the same ponds and under similar experimental conditions, especially rabbit and fish species and age, fishpond dimensions, as well as the fertilisation mode. The fishpond effluent was re-used to irrigate rice fields rather than being discharged into the environment. This study advocated the potential adaptation of rabbits to wetland conditions and the role of rabbit droppings as organic fertilisers in providing a better environment for fish production. On-farm resources, including rabbit droppings, were the main source of nutrients in the system. The analysis of nutrient flow revealed that 27% N and 79% P of the total nitrogen and phosphorus in fertilizing input in fishponds were supplied by rabbit droppings only. Nile tilapia Oreochromis niloticus were able to recover 18.5–37.6% N and 16.9–34.3% P of the total nitrogen and phosphorus inputs, the rest being accumulated in the pond water and the sediment, making them useful for soil fertilisation. The re-use of nutrient-rich effluent in rice irrigation increased rice production, allowing a successful complete substitution of inorganic fertilisers. The irrigation also reduced environmental pollution as the water seeping through rice field was 31.8 and 83.3% less concentrated in total phosphorus and nitrite pollutants, respectively, than was the pond water. Economically, the IRFR generated up to 597% net return over that of the rice inorganically fertilised, thereby substantiating the sustainability of the system. Overall, it is concluded that the IRFR system works well, is readily applicable, and capable of high, diversified, and sustainable production on limited land. As such, the study demonstrates the potentialities of the IRFR system to contribute successfully to poverty reduction, and the enhancement of food security in rural areas. The system promises economic returns and is environmental friendly. The research recommends the optimal range of rabbit density, that is, 800–1200 rabbits per hectare of pond, and the best fish stocking density, that is, 3 fish.mˉ², for a sustainable IRFR culture system. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.