Uncertainty about anaerobic digestion process stability is the main issue preventing more widespread use of the process as a source of energy recovery in wastewater treatment facilities. The overall objective of this research was to study the feasibility of enhancing biogas production inside wastewater facilities using co-digestion of municipal sludge with bakery waste. Another objective was to improve the stability index and a mathematical model that can be useful tools to predict the process stability of municipal sludge digestion alone, and when it is mixed with bakery waste, as a substrate for microorganisms. Experiments were conducted in three phases. In phase 1, a full-scale anaerobic digester at Central Weber Sewer Improvement District, Ogden, UT, receiving a mixture of primary and secondary sludge, was monitored for one hundred days. Chemical oxygen demand (COD), and volatile solids (VS) mass balances were conducted to evaluate the stability of the digester and its capability of producing methane gas. The COD mass balance accounted for nearly 90% of the methane gas produced while the VS mass balance showed that 91% of the organic matter removed resulted in biogas formation. Other parameters monitored included: pH, alkalinity, VFA, and propionic acid. The values of these parameters showed that the digester was running under stable steady state conditions. At mesophilic temperature, the stability index was determined and equal to 0.40 L (CH4)/ g(ΔVS) In phase 2, the feasibility of adding BW to MS was tested in batch reactors scale. The biogas production was enhanced and the digester was stable until the range of 37- 40% of BW to 63-60% of MS. The ADM1 coefficients were modified to accurately predict the digester performance. The modified model outputs (pH, VFA, and methane) were within acceptable ranges when compared with the observed data from the batch reactors. In phase 3, the feasibility of MS and BW were tested using an Induced Bed Reactor (IBR) with a 50:50% ratio of MS:BW (COD basis). The process was stable during different hydraulic retention times and the ADM1 was modified to predict the stability of the process in the IBR.

A liquefação hidrotermal (HTL) é uma tecnologia muito utilizada para a conversão de diversos tipos de biomassa em Bio-óleo bruto; contudo, enquanto tal combustível é produzido uma fase aquosa (PHWW), rica em matéria orgânica e alguns compostos tóxicos, também é gerada, podendo ocasionar severos impactos ambientais negativos. O objetivo da presente pesquisa foi aplicar dois bio-adsorventes: in natura (BAA) e ativado quimicamente (BAAA), derivados da casca de amendoim, como pré-tratamentos da PHWW afim de melhorar sua biodegradabilidade anaeróbia. O carvão ativado granular (GAC) foi utilizado como adsorvente modelo para comparação. Os processos de adsorção foram otimizados com a utilização de desenhos compostos centrais rotacionais (DCCR), no quais as variáveis independentes foram: pH do adsorvato, temperatura e quantidade de (bio) adsorvente no meio. A porcentagem de remoção de DQO e do íon amônio foram as variáveis dependentes. Isotermas de adsorção foram obtidas em ensaios em batelada. Após realizado o estudo do processo de adsorção, o potencial metanogênico dos efluentes pré-tratados e do efluente in natura foi determinado. Esses ensaios foram conduzidos com três concentrações de PHWW (6,5%, 13% e 26%), com dois ensaios controle, um negativo e outro positivo. A pressão nos frascos reatores foi monitorada diariamente e a determinação da composição do biogás produzido foi realizada por cromatografia gasosa uma vez por semana. Os resultados para a processo adsortivo foram encorajadores, uma vez que cada bio-adsorvente testado foi otimizado para diferentes variáveis resposta: BAA (NH4+) e BAAA (DQO). Os ensaios anaeróbios mostraram que uma maior taxa de produção metanogênica, dos efluentes pré-tratados, pode estar ligada à modificação química da superfície nas cascas de amendoim. Foi possível concluir que a bio-adsorção se perfila como uma alternativa sustentável para o pré-tratamento de efluentes advindos da HTL de cianobactérias. / Hydrothermal liquefaction (HTL) is a technology widely used for the conversion of several types of biomass to bio-crude oil; however, while such a fuel is produced an aqueous phase (PHWW), rich in organic matter and some toxic compounds, is also generated and can cause severe negative environmental impacts. The objective of the present research was to apply two bio-adsorbents: peanut bio-adsorbent (PB) and activated peanut bio-adsorbent (APB), as pre-treatments of PHWW to improve their anaerobic biodegradability. Granular activated carbon (GAC) was used as an absorbent model for comparison. The adsorption process was optimized with the use of central rotational composite designs (DCCR), in which the independent variables were: pH of the adsorbate, temperature and amount of (bio) adsorbent in the medium. The percentage of COD removal and ammonium ion were the dependent variables. After the study of the adsorption process, the methanogenic potential of the pretreated effluents and raw PHWW was determined. These trials were conducted with three concentrations of PHWW (6.5%, 13% and 26%), with two control trials, one negative and one positive. The pressure in the reactor flasks was monitored daily and the composition of the biogas produced was determined by gas chromatography once a week. The results for the adsorption process were encouraging, and ach bio-adsorbent tested was optimized for different response variables: PB (NH4+) and APB (COD). The anaerobic assays showed that a higher rate of methanogenic production of pretreated effluents may be linked to the chemical modification of the surface in the peanut shells. It was possible to conclude that the bio adsorption is outlined as a sustainable alternative for the pretreatment of effluents coming from HTL.

<p>In light of constant research regarding the development of alternate fuels, anaerobic digestion of grains diluted in process water from a wastewater treatment plant has been investigaed by starting biogas reactors to produce methane. The possibility of using the sludge from the reactors as fertilizer was also explored. The experiment ran for 90 days of which three days were used to collect samples over a 24-hour period. Variables monitored were associated to process stability, consistency and production. The results of the 24-hour periods show that volatile fatty acids concentrations increase immediately following feeding, peak a few hours later then decrease. Gas production is most efficient at the beginning of the period then stagers after about 20 hours. Results of the 90-day period resemble the 24-hour results; high volatile fatty acid (VFA) concentrations are often linked to low gas production and methane concentrations. The results indicate that certain types of process waters are better suited as dilution liquids than others i.e. digested sludge is better than centrifugation water, though overall gas production in all reactors averaged ca 650 ml/ g volatile solids loaded. With regards to fertilizer use, Cr was the only metal that was measured in unacceptable quantities. Fertilizing the land is not a problem seen from the heavy metals perspective. There is, however, a need for further research and process development before any full-scale digestion processes of this type are initiated.</p>

<p>Biogas, a mixture of methane and carbon dioxide, is produced in the anaerobic digestion of sewage sludge. After anaerobic digestion, the digested sludge is often allowed to degas for one or two days. This gas is seldom utilised, but if the degassing could be accelerated, utilisation would be easier. Ultrasound can be used as a pretreatment method for waste activated sludge. It has a disintegrating effect on the sludge and causes lysis of bacteria in the sludge. It also speeds up the hydrolysis; the limiting step of anaerobic digestion of waste activated sludge. Ultrasound can be used to degas waterbased liquids. Ultrasonic degassing of sewage sludge has not been examined previously. The present study aims to investigate the effect of ultrasound on waste activated sludge as well as the potential of ultrasound to speed up the degassing of digested sludge. A semi-continuous, lab-scale digestion experiment was performed with four reactors: two receiving untreated sludge and two receiving treated sludge. The effect of the sonicator was 420 W and the treatment time was 6 min, which corresponds to an energy input of 8.4 kWh/m³. Total solids (TS) of the waste activated sludge was ~3.5 %. The ultrasonic treatment caused an increase in gas production of 13 %. There was no difference in methane content. The concentration of filterable chemical oxygen demand (fCOD) increased 375 %, or from 2.8 % to 11 % of total COD. In terms of energy loss/gain the increase in gas production resulted in a loss of 2.7 kWh/m³, i.e. more energy is needed to treat the sludge than the potential energy of the increased gas production. However, if the sludge is thickened to a TS >5 %, a net energy gain should be reached. The effect of ultrasound on the degassing of digested sludge was examined in three barrels. The degassing was measured with and without circulation as well as with ultrasonic treatment. The digested sludge had a gas emission rate of 115 L/(m³ day). No direct burst of gas occurred due to ultrasonic treatment. Over two days more gas was emitted from the barrel equipped with ultrasound, probably due to an induced post-digestion. Thus, ultrasonic pretreatment of waste activated sludge increases the biogas yield. It is inconclusive, whether ultrasonic treatment of digested sludge effects the degassing or not.</p>

<p>Phytoremediation as a way to control and lessen nutrient concentrations in landfill leachate is a cheap and environmentally sustainable method. Accumulated nutrients in the plants can then be removed by harvesting and anaerobically digesting the biomass. This study presents two aquatic plants (L. minor (L.) and P. stratiotes (L.)) and one microalgae species (C. vulgaris (L.)), their capacities for growth and nutrient removal in leachate from Häradsudden landfill, Sweden, are investigated. The biogas potential of the two plants is determined via anaerobic digestion in a batch run, followed by a lab-scale reactor run for L. minor only. Results show that growth in leachate directly from the landfill is not possible for the selected species, but at a leachate dilution of 50% or more. Nutrients are removed in leachates with plants to a higher extent than in leachates without, yet the actual amounts do not differ notably between plant species. L. minor proves a better choice than P. stratiotes despite this as growth is superior for L. minor under the experimental conditions of this study. Considering biogas production, L. minor gives more methane than P. stratiotes according to the results from the batch run. The former is however not suitable for large-scale anaerobic digestion unless as an additional feedstock due to practical cultivation issues.</p>

Polychlorinated biphenyls (PCBs) are toxic and persistent anthropogenic contaminants. Concern on their adverse health effects has led to their regulation in air, water and/or soil in addition to sludge. Hence, removal of PCBs in various matrices, including transformer oils (TO) is a priority. This study aims to investigate PCB-118 and Aroclor 1254 toxicity and dechlorination by varying certain critical experimental components including electron donor (sludge or fatty acids), inocula (unacclimated or acclimated culture) and the doses of PCB and TO under anaerobic conditions. Anaerobic toxicity assays (ATA) reactors, lab-scale anaerobic batch digesters and sediment microcosms were used for this purpose. Increase in PCB-118 and TO doses affected anaerobic digester performance by negatively influencing methanogenesis, while favoring dechlorination only with the increase in PCB-118 dose. Up to 22% PCB-118 removal was attained with unacclimated culture. Studies with acclimated cultures showed Grasse River (GR) sediment to be the most active when compared to Fox River and Baltimore Harbor sediments. In GR sediment microcosms, PCB-118 and Aroclor 1254 removal efficiencies decreased when TO was present (1%), while 10% TO inhibited PCB dechlorination. Waste activated sludge was shown to be an effective electron donor, similar to fatty acids. Aroclor 1254 dechlorination was dechlorinated through removal of flanked meta and para chlorines, however, dechlorination pathways appeared to differ according to the presence/absence of TO. No ortho or unflanked chlorines were removed. Molecular tools (qPCR and DHPLC) were used to confirm the presence of active PCB dechlorinators. Dechlorination of PCBs was shown to be growth-linked.

Scum is an integral component of solids management in MWWTP and is composed of fats, oils, grease and other entrained floatable materials that are collected during primary clarification. Lab scale BMP tests showed the addition of 14.5 g VS/L of scum exhibited the greatest increase in biogas production of 1.6 times per g VS added compared to the control, while a higher additional scum loading of 33.7 g VS/L reduced the biogas yield to 32% of the control reactor. Lab scale semi-continuous digestion measured the effects of scum loading and temperature of pretreatment in the scum concentrator. At 15 d and 20 d HRTs the greatest observed improvement in biogas was achieved by adding 3% scum by volume and pretreating the scum at 70°C in a scum concentrator with respective improvements of 24% and 16%.

Anaerobic digestion of excess biological wastewater treatment sludge (WAS) from pulp mills has the potential to reduce disposal costs and to generate energy through biogas production. The organic matter in WAS is highly structured, which normally hinders biogas production. This study investigated three methods of pretreating WAS from two different pulp mills before anaerobic digestion to improve biogas yield and production rate. The three pretreatment methods tested were: i) thermal pretreatment at 170oC, ii) caustic pretreatment at 140oC and pH 12, and iii) sonication at 20 kHz and 1 W/mL. Thermal pretreatment proved to be the most effective, increasing biogas yield by 280% and 50% and increasing production rates 300-fold and 10-fold for the two samples, respectively. Caustic pretreatment showed similar results, but resulted in the formation of soluble non-biodegradable compounds. Sonication was the least effective pretreatment and did not substantially increase biogas yield, but increased biogas production rate.

The development and patenting of a new technology for the anaerobic digestion of solid waste is described. The design basis is explained and justified by extensive reference to the literature. The technology was specifically designed to be versatile, robust and affordable and is directly derived from other proven processes for organic waste management. The ways in which environmental regulations directly affect the development and commercialization of organic waste processing technologies are described. The great differences in regulations between Europe and North America are analyzed to explain why anaerobic digestion is common in Europe and rare in North America and why this is the result of waste management economics which are driven by these regulations. The new technology is shown to be competitive in the Province of Ontario in particular and North America in general; a detailed financial analysis and comparison with European technologies is provided in support of this conclusion.

To improve biogas production from lignocellulosics, methanogenic microbial enrichments were prepared from moose rumen fluid, beaver droppings, and internal circulation (IC) reactor granules amended with cellulose, pine needles, lignosulphonate, tannic acid, and poplar hydrolysate. Tannic acid delayed methanogenesis compared to cellulose only enrichments, both by reducing initial rates (up to 50% in beaver dropping cultures) and increasing lag times (up to 50 days in moose rumen cultures). Biogas yields from poplar hydrolysate were 56 % by beaver droppings, 51% % by IC granules, and 31 % by moose rumen enrichments. Bacterial community profiles, determined via denaturing gradient gel electrophoresis (DGGE) showed divergent populations between enrichments. Enrichment on pine needles or poplar hydrolysate promoted bioconversion of post extraction wash (PEW), and beaver dropping enrichments fed pine needles equaled the yield (about 23%) from IC granules. Together, the DGGE and PEW results provide evidence of acclimatization to previously recalcitrant feeds.