Treatment of metal-contaminated wastewater: a comparison of low-cost biosorbents.

This study aimed to identify some optimum adsorption conditions for the use of low-cost adsorbent, seaweed (Ascophyllum nodosum), sawdust and reed plant (Phragmites australis) root, in the treatment of metal contaminated wastewater for the removal of cadmium, chromium and lead. The effect of pH on the absorption capacity of each of these biosorbents was found to be significant and dependent on the metal being removed. Post-adsorption FTIR analysis showed significant binding activities at the nitro NO groups site in all biosorbents, especially for lead. Competitive metal binding was found to have possibly affected the adsorption capacity for chromium by A. nodosum more than it affected sawdust and P. australis root. Adsorption is believed to take place mainly by ion exchange particularly at low pH values. P. australis root exhibited the highest adsorption for chromium at pH 2, cadmium at pH 10 and lead at pH 7. A. nodosum seaweed species demonstrated the highest adsorption capacity of the three biosorbents used in the study, for cadmium at pH 7 and for lead at pH 2. Sawdust proved to be an efficient biosorbent for lead removal only at pH 7 and 10. No significant effect of temperature on adsorption capacity was observed, particularly for cadmium and lead removal.

Modelling start-up performance of anaerobic digestion of saline-rich macro-algae.

Some of the key factors affecting the adaptation of anaerobic digestion processes to increasing levels of salinity were determined in batch tests using brown seaweed as a feedstock. It was found that cultures seeded with non-saline anaerobic inoculum required an adaptation period of up to two months to reach the same level of methane production rate as in those cultures seeded with saline-adapted inoculum. The Anaerobic Digestion Model No.1 (ADM1) was modified to include an extra inhibition function to account for the effect of salinity, and calibrated using a set of experimental data obtained from batch biochemical methane potential tests. After calibration, the model was able to accurately predict methane production rates. Thus, the results show that, in the absence of saline-adapted inoculum, non-saline inoculum can be used for the start-up of anaerobic digestion systems treating saline-rich feedstocks.

The impact and mode of action of phenolic compounds extracted from brown seaweed on mixed anaerobic microbial cultures.

AIMS: This study discusses the effect of phenolic compounds extracted from brown seaweed (phlorotannins) on mixed microbial cultures found in anaerobic systems. METHODS AND RESULTS: Assays were conducted with phloroglucinol as the nonpolymerized form of phlorotannin and with phlorotannins extracted from the brown seaweed Laminaria digitata. Electron micrographs revealed that phlorotannins induce significant extra- and intracellular effects upon cells, with the disruption of cell membranes observed with most micro-organisms. Microscopy results were further confirmed by cell membrane leakage assays demonstrating that phloroglucinol strongly affects cell membrane permeability. However, cell membrane leakage could not be observed with phlorotannins as the cell suspension immediately started to coagulate and impaired spectrophotometric measurements. CONCLUSIONS: Results suggest that the bactericidal activity of phlorotannins is a function of the level of polymerization of the compounds. By monitoring intermediary compounds during the anaerobic digestion of phlorotannins, it was also found that higher energy consumption is required by micro-organisms for survival under stress induced by phlorotannins. SIGNIFICANCE AND IMPACT OF THE STUDY: The successful anaerobic degradation of brown seaweed is thus likely to be dependant on the concentration of phenolic compounds present and their bactericidal effect on micro-organisms. This is the first article to posit a probable mode of action for the antimicrobial effect of phlorotannins.

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.

Sexual risk behaviour among HIV-positive persons in Kumasi, Ghana.

OBJECTIVES: To assess the prevalence and predictors of sexual risk behaviours among HIV-positive individuals in clinical care in Kumasi, Ghana. DESIGN: Cross-sectional survey of 267 (43 males and 224 females) HIV-positive individuals attending Kumasi South Regional Hospital. METHODS: An interviewer-administered questionnaire was used to asses demographic and health characteristics, HIV/AIDS knowledge, attitudes, and beliefs and sexual risk behaviours. RESULTS: Forty-four percent of the sample reported having sex after testing positive for HIV. Of the 175 participants with regular sex partners, 24% had HIV-positive partners. Majority (67%) had HIV-negative partners (serodiscordant couples) or partners of unknown status. More than half (51%) of the study population with regular sex partners reported that they had unprotected anal or vaginal sex. Participants who scored < 50% on the HIV/AIDS knowledge scale were 90% less likely to have used condoms during their last sexual intercourse. Disclosure of HIV status was associated with protective patterns of condom use (OR=2.2; 95% CI: 1.3-12.9). Participants on ARV were 80% less likely to have used condoms during the last sexual intercourse (OR=0.2; 95% CI: 0.04-0.6). CONCLUSION: The high rates of sexual risk behaviour among HIV-positive individuals in this sample place others at risk of HIV infection. It also places these HIV positive individuals at risk for infection with sexually transmitted infections and super-infection with other HIV strains. These findings highlight the need to integrate HIV prevention in routine medical care in Ghana.

Modelling head losses in granular bed anaerobic baffled reactors at high flows during start-up.

Anaerobic treatment of low strength, high flow wastewaters can only be effective if the technology employed can meet key hydrodynamic requirements: maximising the contact surface area and contact period between the influent substrate and the biomass solids, minimising solid washout from the reactor and minimising the backpressure across the system. Backpressure or head loss is an important hydrodynamic property of gravity-flow packed bed reactors, where the flow is the resultant of frictional forces between the incoming fluid and the solid packing material through which the wastewater percolates. Excessive backpressure caused by high influent flow-rates can reduce the contact surface area and increase the influent head on the upstream side of the biomass bed leading to overflow spills, unstable performance and process failure. This study investigates the factors affecting backpressure across a Granular bed baffled reactor (GRABBR) with variable baffle positions. Experimental results were used to develop a mathematical model to quantify backpressure based on physical characteristics of the seed biomass, fluid-flow conditions and reactor geometry. Results have shown that for a constant flow rate the anaerobic baffled reactor exhibits the least backpressure characteristics when both the upflow and downflow areas are roughly 50% of the total compartmental width.

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.

Comparing the performance of UASB and GRABBR treating low strength wastewaters.

Anaerobic technologies have proved successful in the treatment of various high strength wastewaters with perceptible advantages over aerobic systems. The applicability of anaerobic processes to treat low strength wastewaters has been increasing with the evolution of high-rate reactors capable of achieving high sludge retention time (SRT) when operating at low HRT. However, the performance of these systems can be affected by high variations in flow and wastewater composition. This paper reports on the comparative study carried out with two such high rate reactors systems to evaluate their performances when used for the treatment of low strength wastewaters at high hydraulic rates. One of the two systems is the most commonly used upflow anaerobic sludge blanket (UASB) reactor in which all reactions occur within a single vessel. The other is the granular bed baffled reactor (GRABBR) that encourages different stages of anaerobic digestion in separate vessels longitudinally across the reactor. The reactors, with equal capacity of 10 litres, were subjected to increasing organic loading rates (OLRs) and hydraulic retention times (HRTs) of up to 60 kg COD m(-3) d(-1) and 1 h respectively. Results show that the GRABBR has greater processes stability at relatively low HRTs, whilst the UASB seems to be better equipped to cope with organic overloads or shockloads. The study also shows that the GRABBR enables the harvesting of biogas with greater energetic value and hence greater re-use potential than the UASB. Biogas of up to 86% methane content is obtainable with GRABBR treating low strength wastewaters.

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.

Structural analysis of anaerobic granules in a phase separated reactor by electron microscopy.

This paper discusses the microbial community structure of anaerobic granules and the effect of phase separation in anaerobic reactor on the characteristics of granules. Electron micrographs revealed that the core of anaerobic granular sludge consists predominantly of Methanosaeta-like cells, a key microorganism in granulation process. Granules in the methanogenic dominant zone of the reactor were stable and densely packed with smooth regular surface. On the other hand, granules subjected to acidogenic activities were less stable structures with broken parts and an irregular fissured surface. Anaerobic granules consisted of a vast diversity of species from the outer surface to the core of the granule and possessed a multi-layered structure. Viruses in the granules suggests the presence of bacteriophage in the granular biomass. These could be responsible for destroying cells and weakening the internal structure of granules, and thus possibly causing the breaking of granules. The observation of protozoa-like microorganism on the exterior zone of granular structure is believed to play an important role as bacterial predator and control the growth of bacterial cells. The images observed in this study shows that anaerobic granule harbour diverse number of microbial species, and act differently in acidogenic and methanogenic microbial zones.

Anaerobic digestion of municipal solid wastes containing variable proportions of waste types.

In many parts of the world there are significant seasonal variations in the production of the main organic wastes, food and green wastes. These waste types display significant differences in their biodegradation rates. This study investigated the options for ensuring process stability during the start up and operation of thermophilic high-solids anaerobic digestion of feedstock composed of varying proportions of food and green wastes. The results show that high seed sludge to feedstock ratio (or low waste loading rate) is necessary for ensuring process pH stability without chemical addition. It was also found that the proportion of green wastes in the feedstock can be used to regulate process pH, particularly when operating at high waste loading rates (or low seed sludge to feedstock ratios). The need for chemical pH correction during start-up and digestion operation decreased with increase in green wastes content of the feedstock. Food wastes were found to be more readily biodegradable leading to higher solids reduction while green wastes brought about pH stability and higher digestate solid content. Combining both waste types in various proportions brought about feedstock with varying buffering capacity and digestion performance. Thus, careful selection of feedstock composition can minimise the need for chemical pH regulation as well as reducing the cost for digestate dewatering for final disposal.

The performance of a phase separated granular bed bioreactor treating brewery wastewater.

This study presents the performance characteristics of a plug flow phase separated anaerobic granular bed baffled reactor (GRABBR) fed with brewery wastewater at various operating conditions. The reactor achieved chemical oxygen demand (COD) removal of 93-96% with high methane production when operated at organic loading rates (OLRs) of 2.16-13.38kg COD m(-3)d(-1). The reactor configuration and microbial environment encouraged the acidogenic dominant zone to produce intermediate products suitable for degradation in the predominantly methanogenic zone. Noticeable phase separation between acidogenesis and methanogenesis mainly occurred at high OLR, involving a greater number of compartments to contribute to wastewater treatment. The highly active nature and good settling characteristics of methanogenic granular sludge offered high biomass retention and enhanced methanogenic activities within the system. The granular structure in the acidogenic dominant zone of the GRABBR was susceptible to disintegration and flotation. Methanogenic granular sludge was a multi-layered structure with Methanosaeta-like organisms dominant in the core.

Assessment of morphology for anaerobic-granular particles.

This study shows that a proper assessment of granule morphology is fundamental before applying any mathematical derivation or empirical formula based on the shape factor of anaerobic-granular particles to determine granular characteristics. The granular images and size distribution of samples observed in this study revealed two different dimensions along two axes, which characterize these particles as ellipsoids. In the literature, theoretical-settling velocities and particle-size distribution of anaerobic granules have been calculated by assuming granules as spherical-shaped and using the numerical correlation between the size and settling velocity. This resulted in large deviations in results reported for settling velocities and size distribution calculated by using empirical equations when compared with experimentally measured values. It is believed that, because of the nonspherical nature of these particles, errors have been made in the earlier studies (which considered these particles as spherical), while evaluating granular-physical properties.

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.

Effect of rapid hydraulic shock loads on the performance of granular bed baffled reactor.

This paper describes the performance of a granular bed baffled reactor when receiving unpredictable hydraulic shock loads, which is a frequent occurrence in industrial wastewater treatment plants. Shock loads were created by rapidly increasing volumetric organic loading rates from 2.5 to 20 kg COD m(-3) d(-1), by decreasing (in a stepwise fashion) hydraulic retention time from 48 hrs to 6 hrs. Synthetic wastewater containing glucose as the main organic compound was used in this study. High effluent quality was observed, with soluble COD removal efficiencies of 94% to 97%, during all shock loading conditions at steady state. The reactor appeared to possess high tolerance to rapid hydraulic changes with fast recovery time. Marked phase separation between different microorganisms occurred at high organic loading rate, with acidogenesis and methanogenesis being the respective dominant activities in the upstream and downstream compartments of the reactor. The compartmentalised nature of the reactor and the granular bed structure were believed to be responsible for high reactor stability during overloading conditions. Microbial ecology in the system appeared to favour acetate and butyrate production at high organic loading rate. Granular biomass possessed good settling characteristics, hence encouraging high biomass retention within the system. The dense granular bed in the methanogenic zone acted as a filtration bed for lighter floating non-granular biomass, thus further reducing overall effluent solids concentration. This study demonstrated that the granular bed baffled reactor is a suitable system for treating industrial wastewaters with highly varying rates.

Increasing the fertilizer value of palm oil mill sludge: bioaugmentation in nitrification.

Malaysia is essentially an agricultural country and her major polluting effluents have been from agro-based industries of which palm oil and rubber industries together contribute about 80% of the industrial pollution. Palm oil sludge, commonly referred to, as palm oil mill effluent (POME) is brown slurry composed of 4-5% solids, mainly organic, 0.5-1% residual oil, and about 95% water. The effluent also contains high concentrations of organic nitrogen. The technique for the treatment of POME is basically biological, consisting of pond systems, where the organic nitrogen is converted to ammonia, which is subsequently transformed to nitrate, in a process called nitrification. A 15-month monitoring program of a pond system (combined anaerobic, facultative, and aerobic ponds in series) confirmed studies by other authors and POME operators that nitrification in a pond system demands relatively long hydraulic retention time (HRT), which is not easily achieved, due to high production capacity of most factories. Bioaugmentation of POME with mixed culture of nitrifiers (ammonia and nitrite oxidizers) has been identified as an effective tool not only for enhancing nitrification of POME but also for improving quality of POME as source of liquid nitrogen fertilizer for use in the agricultural sector, especially in oil palm plantations. Nitrate is readily absorbable by most plants, although some plants are able to absorb nitrogen in the form of ammoniun. In this study, up to 60% reduction in HRT (or up to 20% reduction in potential land requirement) was achieved when bioaugmentation of POME was carried out with the aim of achieving full nitrification.