Chlorine-susceptible and chlorine-resistant type 021N bacteria occurring in bulking activated sludges.

Two filamentous bacteria causing bulking in two activated sludges were examined. Investigations using morphological features, staining techniques, and fluorescent in situ hybridization identified both filaments as type 021N. However, an examination of the effect of chlorine on the sludges revealed a chlorine-susceptible type 021N in one sludge and a chlorine-resistant type 021N in the other.

Enhancing the start-up of a UASB reactor treating domestic wastewater by adding a water extract of Moringa oleifera seeds.

Water extract of Moringa oleifera seeds (WEMOS) was used to enhance the start-up of a self-inoculated upflow anaerobic sludge blanket (UASB) reactor treating raw domestic wastewater. Two reactors labelled control (RC) and WEMOS addition (RM) were started without special inoculum. Both reactors were fed continuously for 22 weeks with domestic wastewater containing an average total chemical oxygen demand (COD) of 320 mg O2/l and suspended solid (SS) of 165 mg/l. The reactors operated during the entire experimental period at 29 degrees C and at a hydraulic retention time (HRT) of 4 h. The RM reactor received 2 ml WEMOS per litre of influent. WEMOS solution was prepared on the basis of 2.5% (w/v) ground M. oleifera seeds in water. The results of 22 weeks' operation showed an improvement in the performance of the RM compared to that of the RC. The dosage of WEMOS in the feed (1) shortened the biological start-up period by 20%, (2) increased acidogenic and methanogenic activity by a factor of 2.4 and 2.2 respectively, (3) increased the specific biogas production by a factor of 1.6, (4) favoured fast growth of the sludge bed, and (5) allowed the aggregation of coccoid bacteria and growth of microbial nuclei, which are precursors of anaerobic granulation.

Effect of a water extract of Moringa oleifera seeds on the hydrolytic microbial species diversity of a UASB reactor treating domestic wastewater.

The effect of a continuous supply of a water extract of Moringa oleifera seeds (WEMOS) on the hydrolytic microbial population of biomass grown in mesophilic upflow anaerobic sludge blanket reactors treating domestic wastewater was investigated. The WEMOS-treated sludge had seemingly a wider diversity, with enterobacter and klebsiella as dominant hydrolytic bacteria, compared with the control sludge. Additional tests indicated that various hydrolytic bacteria could degrade WEMOS. It appeared that a continuous supply of WEMOS to an anaerobic digester, treating domestic wastewater, increased the diversity of hydrolytic bacteria and therefore enhanced the biological start-up of the reactor.

Anaerobic digestion technologies for closing the domestic water, carbon and nutrient cycles.

Sustainable wastewater treatment requires that household wastewater is collected and treated separately from industrial wastewater and rainwater run-offs. This separate treatment is, however, still inadequate, as more than 70% of the nutrients and much of the chemical oxygen demand (COD) and potential pathogens of a domestic sewage system are confined to the few litres of black water (faeces, urine and toilet water). Whilst grey water can easily be filter treated and re-used for secondary household purposes, black water requires more intensive treatment due to its high COD and microbial (pathogens) content. Recently developed vacuum/dry toilets produce a nutrient rich semi-solid waste stream, which, with proper treatment, offers the possibility of nutrient, carbon, water and energy recovery. This study investigates the terrestrial applicability of Life Support System (LSS) concepts as a framework for future domestic waste management. The possibilities of treating black water together with other types of human-generated solid waste (biowastes/mixed wastes) in an anaerobic reactor system at thermophilic conditions, as well as some post treatment alternatives for product recovery and re-use, are considered. Energy can partially be recovered in the form of biogas produced during anaerobic digestion. The system is investigated in the form of theoretical mass balances, together with an assessment of the current feasibility of this technology and other post-treatment alternatives.