Effect Of Hydraulic Retention Time On Upflow Anaerobic Fixed Bed Reactor Treatment Of Domestic Wastewater

With growing concerns over the impact of fossil fuel usage on climate change,the consideration of wastewater as a source of renewable energy is growing.Toward this end,there are now many applications of anaerobic treatment processes for domestic wastewater that produce energy in the form of methane,rather than aerobic processes that consume energy.However,anaerobic treatment of domestic wastewater alone has generally not been sufficient to meet stringent effluent requirements for chemical oxygen demand(COD)and suspended solids(SS),thus often necessitating some type of post-treatment.This research was to make municipal sewage up to the low-carbon standard emission and recover energy efficiently by the Upflow Anaerobic Fixed Bed Reactor(UAFBR).Due to domestic wastewater specificity and recalcitrance to the biological treatment the anaerobic sludge acclimatization had been provided for the first 24 th days.To establish favorable conditions for bacterial growth and satisfactory treatment performance the temperature within the UAFBR was set at 30±3oC.The concentration of domestic wastewater was increased threefold.After start-up period predetermined volume of non-acclimatized sponge cubes as filler carrier was added directly into the UAFBR.In current study used reticulated porous polyester–urethane sponge(PUS)cubes 10% of carrier filling rate of total volume of UAFBR gave area for microbial growth.As a result,higher COD removal efficiency was achieved at HRT 12 h.During the experiment,the theoretical dependence is confirmed that with decreasing HRT(in my study to 3h),the removal efficiency is decrease.COD efficiency reached 75 percent.As it's appeared from reactor volume definition hydraulic retention time HRT directly impacts on its dimensions.It's evident that lower HRT contribute to lower capital costs through reduction of the reactor tank size.At lower HRT,the possibility of washout is more prominent.This makes it difficult to maintain the effective number of useful microorganisms in the system.Acetate was major component in the effluent VFAs throughout the test periods.As acetate was the substrate of acetate-utilizing methanogens,the accumulation of acetate suggested that rate-limiting step of anaerobic degradation of the organics of the domestic wastewater in the UAFBR was acetate degradation by acetate-utilizing methanogens.The high acetate accumulated concentration especially at HRT of 6 h was likely due to limitation of acetate-utilizing methanogens in reactor and therefore limited degrading performance and methane productivity from acetate.To decrease the level of accumulated acetate,one of approach would be to allow more acetatedegrading biomass in the reactor.Biogas production declined as HRT was decreased and biogas was mainly composed of methane,carbon dioxide and small fraction of hydrogen,hydrogen sulfide,etc.,based on gas composition analysis.The methane gas generated per gram of COD was higher 7g/d at HRT 6h than 4.14g/d 3h or 4.25g/d at 12 h.In this study,approximately 50% of the COD was converted into methane,i.e.about 75% of methane was collected in a gaseous phase while the remaining about 25% was dissolved in the liquid phase.It is clear that methane production at 30±3oC saves 27 % of electricity.Excess sludge production is estimated to be less than in conventional aerobic treatment facilities up to 58 %.The treated wastewater can be reused as reclaimed water and it will lead to increasing of water-reuse up to 68 %.