No description available.

No description available.

No description available.

This thesis presents a chemical, microbiological and mathematical analysis of an anaerobic baffled reactor (ABR) treating domestic wastewater. The purpose of this study was to gain an understanding of the mechanisms of treatment of domestic wastewater in an ABR at pilot-scale, and to use this understanding to develop some guidelines for the design of ABR technology for the anaerobic treatment or pre-treatment of domestic wastewater. Previous research has been undertaken on ABR technology, but no detailed studies of the performance of an ABR on domestic wastewater at pilot-scale have been reported. In this thesis, operating data from a 3 000 ℓ pilot-scale ABR are presented and analysed. Two hypotheses were proposed: that (i) the baffled design of the reactor would facilitate phase separation whereby acidogenic and methanogenic processes predominate in different physical locations in the reactor; and (ii) the critical design parameter is the applied hydraulic retention time. The principle findings of this research were: • The pilot-scale ABR functioned as a solids retention device. Particulate material was retained through settling in the first compartment, forming a gel-like matrix. Reduction of solids occurred through anaerobic conversion to CH4 and CO2. • Partial phase separation of acidogenic and methanogenic communities was observed. • The major factor that controlled biomass washout rate and therefore reactor performance was upflow velocity in each compartment. At higher upflow velocities, slow growing microorganisms failed to establish, resulting in increased solids accumulation rates, while at lower upflow velocities, stable digestion proceeded. • Relatively poor treatment rates were obtained due to the low inherent alkalinity of waters in eThekwini municipality resulting in low operating pH values. • Insufficient pathogen reduction was observed indicating that post-treatment of effluent would be required. It was concluded that the benefit of the baffled design was related to the system’s solids retention characteristics and that the critical design parameters for an ABR domestic wastewater treatment unit were compartment upflow velocity and applied hydraulic retention time. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2009.

Access to modern energy is essential to achieve sustainable development and poverty reduction. However, with about 321 kWh per capita, Rwanda is ranked among the countries that have a lower consumption of primary energy in the world. More than 86 percent of its total energy comes from the traditional biomass energy such as forests, agricultural residues and by-products from crops that lead to environmental degradation and ecological imbalance and negative impacts on human health as well. In addition, only 301,500 ha of forest are available for fuel wood and other uses such as construction for a total population of 10.5 million. Therefore, decentralized energy sources in small-scale are presented to improve access to "appropriate" energy, which are beneficial to human health and environmental perspectives. The anaerobic digestion of biomass, popularly called “biogas”, is one of the appropriate energy technologies for cooking and/or lighting purposes (both in households and in institutions), which receives special attention in Rwanda since 2007. Three main objectives of this study were to assess the current biogas sector in Rwanda, to make projections of biogas development by 2020 and finally to analyze the socio-economic and environment benefits of biogas use to the Rwandan community. The fieldwork conducted in two districts per province in addition to services that are in the capital, was based on the structured questionnaire, discussion with key people and see the state of biogas built. Therefore, in this study we used the "Appropriate Energy Model” to measure the degree of biogas dissemination, which educates for “geographical, institutional, entrepreneurial and socio-cultural “aspects. The results showed that the temperature conditions in the country are generally conducive to the operation of a digester. However, the drought period between June and August, water scarcity in some regions and a low potential for digester feeding impede the propagation of biogas to a large number of people.  The Rwandan entrepreneurs do not face institutional barriers to start-up biogas companies since the bureaucratic system in registration of a company is transparent. The installation costs of biogas plant are so high that they hamper the dissemination of biogas; however biogas technology does not contradict the socio-cultural conditions of Rwandans. Based on projections of potential biogas in Rwanda in 2020, following three scenarios for 2020 biogas development were identified: 1,135,000 biogas plants can be built in 2020 by considering a global basis the potential biogas available If 70% of the population will live in grouped settlements in 2020, 70% of Rwandan households will use biogas if additional resources as livestock and subsidies were provided to the poor families. Only 10% of the population (251,000households) will be eligible for biogas installation Reducing the consumption of firewood after biogas operation provides annual coverage of approximately 0.306 ha of forest area per household. Therefore, each household biogas would reduce annual GHG emissions of about 4.1 tonnes of CO2 and could possibly lead to Rwanda an annual income of about USD 21 due to the reduction of CO2 emissions in a hypothetical rate USD 5 per ton of CO2 if registered under the CDM.

Hyperthermophiles are microorganisms that can grow at temperatures close to the boiling point of water or above. They are potential resources of thermostable enzymes including alcohol dehydrogenases (ADHs). Both Thermococcus guaymasensis and Thermotoga hypogea produce ethanol as an end product using glucose as substrate. However, the metabolic pathway and enzymes involved in alcohol production by these hyperthermophiles were not clear. ADH is a key enzyme responsible for alcohol metabolism, and the enzyme has been purified and characterized. T. hypogea is an extremely thermophilic anaerobic bacterium capable of growing at 90??C. The NADP+-dependent ADH from T. hypogea was purified to homogeneity and a homodimeric protein with a subunit size of 40 ?? 1 kDa. A part of its encoding gene was cloned and sequenced, from which a major part of the amino acid sequence of the enzyme was deduced and found to have high similarities to iron-containing ADHs from other Thermotoga species and harbored typical iron and NADP+-binding motifs. The conserved domain search showed that T. hypogea ADH was a member of the family of uncharacterized iron-containing ADHs. The iron content of the enzyme was determined to be 1.02 ?? 0.06 g-atoms per subunit. It is the first characterized iron-containing ADH from hyperthermophilic bacteria. Similar to known iron-containing ADHs, T. hypogea ADH was oxygen sensitive; however, the loss of enzyme activity upon exposure to oxygen could be recovered by incubation with dithiothreitol and Fe2+. The enzyme was thermostable with a half-life of about 10 h at 70??C, and its catalytic activity increased along with the rise of temperatures up to 95??C. Optimal pH values for the production and oxidation of alcohol were determined to be 8.0 and 11.0, respectively. The enzyme had a broad specificity in utilizing primary alcohols and aldehydes as substrates. Apparent Km values for ethanol and 1-butanol were much higher than that for acetaldehyde and butyraldehyde and thus the enzyme was likely to catalyze the reduction of aldehydes to alcohols in vivo. T. guaymasensis is a hyperthermophilic anaerobic archaeon capable of catalyzing the starch degradation and producing ethanol and acetoin as end-products. The purified T. guaymasensis ADH was an NADP+-dependent homotetramer with a subunit of 40 ?? 1 kDa. The enzyme was a primary-secondary ADH, but it exhibited substrate preference on secondary alcohols and corresponding ketones. In particular, it catalyzed the reduction of diacetyl to 2, 3-butanediol via acetoin in which the reduction from diacetyl to acetoin was irreversible. For the oxidation of 2, 3-butanediol, the enzyme exhibited higher activities on (2R, 3R)-(-)-2, 3-butanediol and meso-2, 3-butanediol than (2S, 3S)-(+)-2, 3-butanediol while the stereoselective reduction of racemic (R/S)-acetoin produced (2R, 3R)-(-)-2, 3-butanediol and meso-butanediol but not (2S, 3S)-(+)-2, 3-butanediol. The optimal pHs for the oxidation and formation of alcohols were determined to be 10.5 and 7.5, respectively. The enzyme activity increased along with the rise of temperatures up to 95??C, and it was highly stable with a half-life of 24 hours at 95??C. The enzyme was resistant to 30% (v/v) methanol (retaining 40% of its full activity). NADPH for the ketone reduction was efficiently regenerated using isopropanol as a substrate. The apparent Km value for NADPH was 40 times lower than that of NADP+, and the specificity constant with NADPH were 5 times higher than that of NADP+. Therefore, the physiological role of the enzyme was likely to be responsible for the reactions involving the NADPH oxidation???coupled formation of ethanol and/or acetoin. The fully active T. guaymasensis ADH contained 0.9 ?? 0.03 g atom zinc per subunit determined by inductively coupled plasma mass spectrometry (ICP-MS) and was the first characterized zinc-containing ADH from Thermococcus species. The gene encoding this enzyme was cloned and sequenced, and the deduced amino acid sequence contained 364 amino acids showing high similarities (85%) to those ADHs from Thermoanaerobacter species which have only the catalytic zinc atom. The motif analyses also indicated the enzyme lacked of the structural zinc-binding motif; thus, zinc might play a catalytic role in the enzyme. Further analyses showed the presence of the conserved domains of L-threonine dehydrogenases; however, the enzyme could not oxidize L-threonine or L-serine. Distinct from most of zinc-containing ADHs, the enzyme activity was almost fully inhibited by 100 ??M Zn2+ in the assay mixture. Moreover, it was sensitive to oxygen. An NADP+-dependent ADH was purified from the hyperthermophilic anaerobic archaeon Thermococcus strain ES1, an ethanol producer. The recombinant enzyme over-expressed in Escherichia coli was purified using a two-step procedure including heat treatment, and characterized in comparison with the native enzyme. The purified recombinant enzyme exhibited a specific activity of 52.8 U mg-1, close to that of the native enzyme (57 U mg-1). Both native and recombinant enzymes were homotetramers with a subunit size of 45 ?? 1 kDa. Their optimal pHs for the ethanol oxidation and acetaldehyde reduction were determined to be 10.5 and 7.0, respectively. Both enzymes were able to oxidize a series of primary alcohols and diols. Metal contents of the fully active recombinant enzyme were determined by ICP-MS to be 1.0 ?? 0.04 g atom iron per subunit, and both iron-containing enzymes were oxygen sensitive. Their kinetic parameters showed lower Km-values of acetaldehyde and NADPH than those of ethanol and NADP+, suggesting the native enzyme could be involved in ethanol formation in vivo. The recombinant and native enzymes had almost identical characteristics and thus its encoding gene was successfully over-expressed in E. coli. The deduced amino acid sequence of the ADH from Thermococcus strain ES1 was a 406 amino acid polypeptide. Its amino acid sequence showed high identities (80%) to iron-containing ADHs from the related archaea Thermococcus zilligii and Thermococcus hydrothermalis. The conserved domain search revealed it belonged to the family of iron-containing ADHs. Moreover, the sequence of the enzyme had catalytic metal and dinucleotide-binding motifs typical for iron-containing ADHs. In conclusion, the results indicate that iron- and zinc-containing ADHs from hyperthermophiles have significant differences in terms of biophysical, biochemical and molecular properties. The hyperthermophilic bacterial and archaeal iron-containing ADHs are divergent while the zinc-containing ADH from T. guaymasensis has significant similarity to thermophilic bacterial ones.

The rate of anaerobic digestion (AD) often depends on the rate-limiting hydrolysis step that makes organics available to microorganisms. To achieve efficient conversion of particulates to soluble materials and finally methane, the biomass in the digester must be provided with optimal operational conditions that will allow for biomass retention and substrate metabolism. Two approaches were employed in this study to improve the ultimate biodegradability of waste activated sludge (WAS) - Pre-treatment (PT) and operation using an Anaerobic Membrane Bioreactor (AnMBR). PT of WAS is one way of speeding up hydrolysis. It has been proposed that PT leads to the lysis of cells, which in turn causes the release and solubilisation, and thus availability of intracellular matter to microorganisms for microbial growth and metabolic activities. This study compared the effect of thermal, sonication, and sonication + hydrogen peroxide PT on chemical oxygen demand (COD) solubilisation of WAS. Based on the soluble COD (SCOD) release, it was concluded that combined chemi-sonic treatment resulted in better WAS degradation rather than individual ultrasonic pre-treatment and thermal PT. The highest solubilisation rate was observed at a chemi-sonic PT of 50gH2O2/kgTS and sonication duration of 60 minutes. At this PT, a COD solubilisation of 40% was observed which was significantly different than PT involving only sonication and no pre-treatment (0.88%) at 95% confidence. Therefore a peroxide-sonic PT was chosen to treat WAS in this study as it was expected to result in the greatest improvement in WAS biodegradability. In addition to PT, biodegradability of WAS can also be improved by coupling PT with an AnMBR. AnMBRs prevent biomass washout by decoupling the solids retention time (SRT) from the hydraulic retention time (HRT). Thus, a long SRT can be used to provide sufficient duration for biological activities without increasing the volume of the reactor. In this study, a 4.5L AnMBR with an HRT and SRT of 3 and 20 days, respectively was used to treat raw and PT WAS. In order to compare the biodegradability of PT and raw WAS, the AnMBR was operated in three phases. Phase 1 was operated with raw WAS, Phase 2 was operated with WAS pre-treated with 50 gH2O2/kgTS and 20 minutes ultrasound (US), and Phase 3 was operated with WAS pre-treated with 50 gH2O2/kgTS and 60 minutes US. The anaerobic biodegradability of WAS following a combination of ultrasonic pre-treatment and H2O2 addition was significantly improved, with Phase 3 resulting in the greatest improvement. The COD destruction for phases 1, 2, and 3 were 49%, 58%, and 63%, respectively whereas the volatile suspended solids (VSS) destruction for phases 1, 2, and 3 were 46%, 71%, and 77% respectively. Organic Nitrogen (Org-N) destruction increased from 44% to 52% for phases 1 and 2 respectively. A further increase of 18% in Org-N destruction was observed in phase 3. This improvement in biodegradability of WAS was attributed to the high solubilisations of COD, VSS, and ON and conversion of non-biodegradable materials to biodegradable fractions. In order to determine the effect of PT of WAS on membrane performance, the transmembrane pressure (TMP) and fouling rate were monitored throughout the operation of the AnMBR. Negligible variation in membrane performance was observed over all three phases. At a constant low flux of 2.75 litres/m2/hour (LMH), the TMP and the fouling rate remained low over the course of operation. In order to maintain the performance of the membrane, maintenance cleaning with 50 ml of 2g/L critic acid solution followed by 50 ml of 0.2 g/L sodium hypochlorite was performed three times a week. In addition, a gas sparing rate of 2 L/minute and a permeation cycle of 10 minutes with 8 minutes of operation followed by 2 minutes of relaxation was employed. During phase 2 of this study, a new membrane was installed due to a faulty gas sparging pump. A slight decrease of TMP was observed with the installation of the new membrane; however the decrease was minimal. In addition critical flux for phases 2 and 3 were determined to be in the range of 6 to 12 LMH. In conclusion, the incorporation of H2O2-US PT with AD could allow treatment plants to substantially reduce the mass flow of solids and organics and thus result in a decrease in requirements for downstream sludge processing. With sufficient maintenance, steady operation could be achieved for a hollow fibre AnMBR with a total solids concentration range of 20-25 g/L, an HRT of 3 days, and an SRT of 20 days. It was found that PT could be successfully integrated with AnMBR to substantially reduce the HRT required for digestion when compared to conventional designs.

No description available.

Two different types of sludges from two popular sewage treatment systems were used in this study; namely, anaerobic pond sludge from a wastewater stabilisation pond system and filter pressed primary sludge from a primary sewage treatment plant. Under Egyptian conditions, Ascaris eggs represent the main health concern for sludge application on land and, accordingly, the effect of sand drying beds and a passive composting system (using agricultural wastes as bulking agents and cement dust as an additive to the sludge) were studied in terms of the inactivation of Ascaris eggs. From the characterisation and assessment of the anaerobic pond sludge from the Mit Mazah wastewater stabilisation pond system, it has been concluded that the sludge was well digested and free of viable Ascaris eggs. Consequently, this sludge is considered to be safe for land application, after appropriate dewatering. For the purposes of the study, anaerobic pond sludge was seeded with Ascaris vitilorum eggs (cattle ascarid). Within 30 days of dewatering on sand drying beds during the winter season (October and November), the Ascaris eggs were found to be inactivated only in the top layers, where the average solids content was approximately 85%. By the end of the two month drying period, the middle and bottom layers of sludge on the drying beds contained an average solids content of 74% to 77% and 72 to 73%, respectively, yet viable Ascaris eggs were still detected. During a second sludge application during the winter season (December and January), unfavourable weather conditions prevailed and, by the end of the 60 days drying period, total solids content averaged 54% in the top layer of sludge. The middle and bottom layers had an average total solids content of 49% and 44%, respectively. Throughout the winter drying period, all samples collected were positive for viable Ascaris eggs throughout the full depth of sludge. However, during the summer season, samples collected from the drying beds after 17 days of drying did not contain viable Ascaris eggs in the top sludge layers, where the solids content ranged from 74% to 63%. After one month of summer drying, no viable Ascaris eggs were detected throughout the entire depth of sludge on the drying beds and the lowest solids content recorded was 80% for the bottom layers. From this study, it can be concluded that, during the wet season in Egypt, drying beds were not efficient in destroying Ascaris eggs throughout the entire sludge depth. During the summer season, Ascaris eggs can be inactivated much more rapidly, compared to the winter season. Desiccation does not seem to be the only factor influencing the destruction of Ascaris eggs, with sludge temperature, solar radiation intensity and exposure time being possible major factors. By comparing the composting of filter pressed primary sludge in passive and windrow piles (used as control piles), it has been proved that the passive composting system is much more efficient in maintaining regular high temperatures in the composting mixture for a much longer duration (additional 10 days), due to the favourable aerobic conditions. Moreover, passive composting preserves the nitrogen content through the naturally controlled internal temperature, less need for turning and lower loss of moisture. By the end of the composting process, the total nitrogen content for the passive and windrow piles was a gain of 17.5% and a loss of 0.7%, respectively, while the ammoniacal nitrogen content in the product was 1109 mg/l and 837 m/l, respectively. From the hygienic point of view, passive composting technology proved to be much more effective in inactivating Ascaris eggs present in the primary sludge, compared to the windrow pile system. Viable Ascaris eggs were not detected after 30 days of composting using the passive system, compared with 60 days of composting for the windrow pile. Industrial cement dust as an additive and agricultural wastes (from fennel and basil production) were incorporated with sludge to form a range of composing mixtures. From the sludge/cement dust composting piles with agricultural wastes as bulking agent, it can be concluded that more than 35% concentration of cement dust was unfavourable for the decomposition process, due to the high pH and high temperature levels attained as a result of the effect of cement dust and dehydration of the organic matter. Moreover, loss of nitrogen was very high, due to the release of ammonia, encouraged by the high pH and high temperature in the composting mixture. The passive composting system was very efficient in naturally controlling the internal temperature in all the sludge/cement dust piles with bulking agent. Excessive heat was released to the atmosphere through the chimney effect created by the circulation of air through the perforated pipes and upwards into the pile. Internal temperatures for even the piles with the highest proportion of cement dust did not exceed 73°C. Inactivation of Ascaris eggs was achieved after only 15 days of composting for all the different cement dust concentrations, mainly due to the influence of high pH and high temperature levels for long periods but may also be due to the high release of ammonia gas. The passive composting of sludge amended with 30% cement dust without bulking agent was inefficient for both the decomposition process and inactivation of Ascaris eggs. No biological activity was taking place during the two months fermentation stage, due to the prevailing anaerobic conditions (lack of air voids and high moisture content) By considering all the different parameters for evaluating a treated compost, including the stability, maturity, nutrient content, heavy metals content and viable Ascaris eggs content for the sludge/cement dust piles with bulking agent, it can be concluded that more than 30% cement dust concentration would be unfavourable, according to the relatively high loss of nitrogen. More than 35% cement dust concentration is certainly unfavourable, mainly as a result of the delay of the decomposition process, the elongation of the composting period and the high loss of nitrogen content. There is no need to separate out the agricultural waste bulking materials after composting because they are organic in nature. Likewise, there is no need to consider separating out the cement dust, as the physicochemical analysis of the final sludge/cement compost with bulking materials showed its suitability for adding to agricultural land as an amendment. In conclusion, sand bed drying is considered to be a suitable process for dewatering of anaerobic stabilisation pond sludge in Egypt and, for extended periods between pond desludging of the order of 6 years, the dewatered sludge will be suitable for direct application to agricultural land. Passive composting is an appropriate technique for preparation of Egyptian filter pressed primary sludge for safe application to agricultural land. Cement dust additions of less than 30% concentration, to the composting mixture in a passive composting system produces sanitised and mature compost. The potential for co-disposal of agricultural wastes and cement kiln dust as bulking agents and additive, respectively, with sewage sludge in the production of compost, is very promising to produce a safe and beneficial outcome to the community.

This study evaluates the enhancement of anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) by microwave pretreatment (MW) at high temperatures (115, 145 and 175°C). The highest level of solubilization was achieved at 175ºC, with a supplemental water addition of 30% (SWA30). Pretreatments combining two modalities; MW heating in presence or absence of hydrogen peroxide (H2O2) was also investigated. Biochemical methane potential (BMP) tests were conducted on the whole OFMSW, as well as on the liquid fractions. The whole OFMSW pretreated at 115 and 145 ºC showed little improvement in biogas production over control. When pretreated at 175 ºC, biogas production decreased due to formation of refractory compounds, inhibiting digestion. For the liquid fraction of OFMSW, the effect of pretreatment on the cumulative biogas production (CBP) was more pronounced for supplemental water addition of 20% (SWA20) at 145 ºC. Combining MW and H2O2 modalities did not have a positive impact on OFMSW stabilization and enhanced biogas production. Based on the BMP assay results, the effects of MW pretreatment (145 ºC) on the AD of OFMSW (SWA20) were further evaluated in single and dual stage semi-continuous digesters at hydraulic retention times (HRTs) of 20, 15, 12 and 9 days. Overall, MW pretreatment did not enhance the AD of the whole waste at the HRTs tested. However, the use of a dual stage reactor digesting non pretreated whole OFMSW had the best performance with the shortest HRT of 9 days. Conversely, for free liquid after pretreatment in two stage reactors at 20 day HRT methane production was tripled. In general, the performance of the dual stage digesters surpassed that of the single stage reactors. Cyclic BMP assays indicated that using an appropriate fraction of recycled effluent leachate can be implemented without negatively effecting methanogenic activity and biogas production. Based on the results obtained in this study, digestion of OFMSW by dual stage reactors without pretreatment appears to provide the best potential for waste stabilization in terms of biogas production and yield, process stability and volumetric loading rates.