Joseph C. Akunna

Nitrate and nitrite reductions with anaerobic sludge using various carbon sources: Glucose, glycerol, acetic acid, lactic acid and methanol

Abstract Batch-tests were used to determine the potentials of digested sludge to reduce nitrate and nitrite in the presence of five different carbon sources: glucose, glycerol, acetic acid, lactic acid and methanol. Ammonium accumulation was found in glucose and glycerol media. Dissimilatory reduction to ammonium accounted for up to 50% of reduced nitrate and nitrite. The rest were denitrified. In the media containing these carbon substrates volatile fatty acids, particularly acetic acid, were produced and ammonification was higher than denitrification activities only when glucose and glycerol were still present in the media. Ammonium production was higher in nitrite cultures than in nitrate cultures. In the culture media with acetic and lactic acids and methanol, ammonium was not detected. Nitrate/nitrite reduction in acetic and lactic acids media was essentially denitrification activity. Up to 100% of reduced nitrate and nitrite in the culture media with these acids were denitrified at average rates between 27 and 23 mg N-NOx/g MLVSSh, nitrite reduction rate being about 14% lower than total nitrate reduction rate. COD requirements for nitrate and nitrite reductions were generally lower in cultures with acetic and lactic acids than in glucose and glycerol cultures. Methanol culture media showed a very small reduction rate for the N-NOx indicating the absence (or presence in very small quantity) of the bacteria capable of denitrifying with this substrate.

Denitrification in anaerobic digesters: Possibilities and influence of wastewater COD/N‐NOX ratio

Abstract Laboratory‐scale completely‐stirred anaerobic digesters were fed with synthetic wastewaters containing nitrate and nitrite and with glucose as the only source of organic carbon in order to investigate and compare the denitrification potentials of anaerobic digesters in the presence of nitrate and nitrite. Varying the input nitrate and nitrite concentration at fixed COD and HRT, methane production without denitrification occurred at COD/N‐NOX > 53; denitrification and methane production at 8.86 ≤ COD/N‐NOX ≤ 53 and only denitrification at COD/N‐NOX 53, ammonification appeared to be the main nitrate and nitrite reduction pathway. The successful competition of ammonia formers over the true denitrifiers at high ratios was attributed to the low initial nitrate and nitrite concentrations.

Stimulation of bioprocesses by ultrasound

Ultrasound (US) has become a ubiquitous technological process in a large variety of scientific disciplines. However, little information exists on the use of ultrasound to enhance biological processes and/or processing and consequently this paper provides an overview of work reported to date on this topic. This review provides a brief introduction to ultrasound and the history of ultrasound as applied to bioprocesses. This is followed by a discussion of the influence of US on discrete enzyme systems, enzymes used in bioremediation, microbial fermentations and enzymatic hydrolysis of biopolymers. Augmentation of anaerobic digestion by US is then considered along with enhancement of enzymes in food science and technology. The use of ultrasonically stimulated enzymes in synthesis is then considered and other relevant miscellaneous topics are described. It is concluded that the precise mechanism of action of US in bio-processing remains to be elucidated though a variety of plausible suggestions are made.

Performance of a granular-bed anaerobic baffled reactor (GRABBR) treating whisky distillery wastewater

Abstract This paper reports the performance of a granular-bed anaerobic baffled reactor (GRABBR) used in the treatment of a whisky distillery wastewater. The results reveal that the system was very effective in the treatment of the high-strength wastewater. Its effectiveness stemmed from process stability created by phase separation promoted by the reactor configuration. It combined the advantages of baffled reactor systems and upflow anaerobic sludge blanket (UASB) systems. Up to 80% COD (or 90% BOD) removal was observed for an organic loading of 4.75 kg COD/m 3 day. It was also found that acidogens were mostly non-granular while methanogens were granular. The GRABBR encouraged phase separation, and consequently the establishment of separate zones for granular and non-granular sludge. The system also showed very high solids retention with effluent suspended solids concentration of about 80 mg/l for all organic and hydraulic conditions studied. This was attributed to the occurrence of granular methanogens in zones (or compartments) downstream of zones occupied by non-granular acidogens.

Investigating the effects of anaerobic and aerobic post-treatment on quality and stability of organic fraction of municipal solid waste as soil amendment

The use of OFMSW for biogas and compost production is considered as a sustainable strategy in saving valuable landfill space while producing valuable product for soil application. This study examines the effects of anaerobic and aerobic post-treatment of OFMSW on the stability of anaerobic digestate and compost and soil quality using seed germination tests. Anaerobic digestion of OFMSW was carried out for fifteen days after which the residual anaerobic digestate was subjected to aerobic post-treatment for seventy days. Seed germination tests showed that fresh feedstock and digestates collected during anaerobic digestion and during the early stages of aerobic post-treatment were phytotoxic. However, phytotoxic effects were not observed in soils amended with the fully stabilised anaerobic digestate compost, ADC. It was also found that seed germination increases with dilution and incubation time, suggesting that lower soil application rates and longer lag periods between soil application of ADC and planting can reduce the amount of biodegradable organics in the ADC, thus enhancing the benefits of ADC as soil amendment.

Nitrate reduction by anaerobic sludge using glucose at various nitrate concentrations: ammonification, denitrification and methanogenic activities

Abstract A synthetic wastewater containing glucose as the sole source of carbon was used to assay glucose‐acclimatized anaerobic digester sludge in batch‐tests for its potential to carry out ammonification (nitrate‐ ‐> ammonium), denitrification (nitrate —>nitrogen gas) and to continue anaerobic digestion processes at various nitrate loads. Nitrate—>ammonium reduction activity was found to increase with decrease in the initial nitrate load. This activity appeared to take place principally during the acidogenesis of the glucose. Nitrate/nitrite loss after the fermentation process was essentially through denitrification. The denitrification capacity of the anaerobic sludge used was very high. Up to 80% of added nitrate was denitrified. The presence of nitrate or nitrite enhanced the fermentation of glucose to acetic acid but inhibited the production of propionic acid and methane. This inhibition was not observed after the complete reduction of nitrate and nitrite.

Carbon and nitrogen removal in a granular bed baffled reactor

The application of an anaerobic five compartment granular bed baffled reactor (GRABBR) was investigated with brewery wastewater for combined carbon and nitrate removal, with a separate downstream nitrification unit for converting ammonia to nitrate. The GRABBR was operated at an organic loading rate of 3.57 kg chemical oxygen demand (COD) m−3 d−1 and ammoniacal nitrogen (NH4-N) loading rate of 0.13 kg NH4-N m−3 d−1 when nitrified effluent from a downstream nitrification unit was recycled to the feed point of the GRABBR. Carbonaceous matter and nitrate were removed simultaneously in the GRABBR at different recycle to influent ratios (from 1 to 2), with nitrogen oxide (nitrate and nitrite nitrogen, NOx-N) loading rates varying from 0.04 to 0.05 kg NOx-N m−3 d−1. At all recycle to influent ratios, COD removal efficiency of 97% to 98% were observed in the GRABBR, and over 99% by the two-stage treatment configuration (i.e. GRABBR and nitrification unit). All the nitrates added to the GRABBR were denitrified in the first three compartments of the system. For all the recycle to influent ratios studied, almost all ammonia was converted to nitrate nitrogen with only small traces of nitrite nitrogen in the nitrification unit. Methane production was observed throughout the experimental period with its composition varying from 25% to 50%, showing that simultaneous methanogenesis and denitrification occurred. This study shows that a GRABBR could bring about a high degree of carbon and nitrate removal, with simultaneous methanogenesis and denitrification, due to plug flow granular bed multi-stage characteristics of the bioreactor.

Modelling sodium inhibition on the anaerobic digestion process

Sodium is a known process inhibitor in anaerobic systems and impacts on methanogens through an increase of osmotic pressure or complete dehydration of microorganisms. In this study, a combination of experimental and modelling approaches has been employed to determine and simulate sodium inhibition on the anaerobic digestion process. The ADM1, which has been successfully used in modelling anaerobic processes, has been modified to include an extra inhibition function that considers the effect of sodium on acetoclastic methanogens and the impact on biogas production and composition. A non-competitive inhibition function was added to the rate of acetate uptake for the model to take into account sodium toxicity. Experimental studies consisted of both batch and reactor tests to obtain parameters for model calibration and validation. The calibrated model was used to predict the effect of ammonia nitrogen on sodium toxicity. It was found that relatively low sodium levels can bring about significant levels of process inhibition in the presence of high levels of ammonia. On the other hand, where the concentration of ammonia is relatively low, the tolerance threshold for sodium ions increases. Hence, care must be taken in the use of sodium hydroxide for pH adjustment during anaerobic digestion of protein-rich substrates.

Mangrove vulnerability modelling in parts of Western Niger Delta, Nigeria using satellite images, GIS techniques and Spatial Multi-Criteria Analysis (SMCA)

Mangroves are known for their global environmental and socioeconomic value. Despite their importance, mangrove like other ecosystems is now being threatened by natural and human-induced processes that damage them at alarming rates, thereby diminishing the limited number of existing mangrove vegetation. The development of a spatial vulnerability assessment model that takes into consideration environmental and socioeconomic criteria, in spatial and non-spatial formats has been attempted in this study. According to the model, 11 different input parameters are required in modelling mangrove vulnerability. These parameters and their effects on mangrove vulnerability were selected and weighted by experts in the related fields. Criteria identification and selection were mainly based on effects of environmental and socioeconomic changes associated with mangrove survival. The results obtained revealed the dominance of socioeconomic criteria such as population pressure and deforestation, with high vulnerability index of 0.75. The environmental criteria was broadly dispersed in the study area and represents vulnerability indices ranging from 0.00–0.75. This category reflects the greater influence of pollutant input from oil wells and pipelines and minimal contribution from climatic factors. This project has integrated spatial management framework for mangrove vulnerability assessment that utilises information technology in conjunction with expert knowledge and multi-criteria analysis to aid planners and policy/ decision makers in the protection of this very fragile ecosystem.

Anaerobic digestion of distillery spent wash: Influence of enzymatic pre-treatment of intact yeast cells.

The potential benefits of enzymatic digestion of intact yeast cells on anaerobic digestion of Scotch whisky distillery spent wash and pot ale were investigated. Various yeast cell wall hydrolytic enzymes were studied based on their effect on dissolution of cell wall glucan and mannoprotein. The synergistic activity of beta-glucanase and protease showed greater than 90% yeast cell digestion at 37 degrees C in 24h. The widely-used industrial enzyme papain showed 95% yeast cell digestion in spent wash at 1% enzyme concentration within 22h at 50 degrees C. Anaerobic digestion of pot ale residues containing intact yeast cells pre-treated with lytic enzymes showed COD reductions of 87%, compared with only 13% without enzymes. Similar results were observed with distillery spent wash centrate. The hydrolysis of intact yeast cells in distillery liquid residues was found to be a rate-limiting step in anaerobic treatment of such residues.