Ecological Responses Of Hydrogen-producing Acetogens To OLR And PH In UASB And ABR Systems

Environmental pollution and the energy crisis are two problems that plaguedthe sustainable socio-economic development and human survival. Anaerobicbiotechnology has become an important route to solve environmental pollution andenergy shortage. How to enhance the efficiency and the stability of anaerobicbiotechnology are the key issues to be solved in the current. The study of anaerobicbiological theory is foundation to develop new technology and impove theefficiency and stability of anaerobic reactors. Organic load rate (OLR) and pH werevery important operation control parameters of anaerobic reactors, and whichchanges will impact on microbial community structure and furth affect theefficiency of anaerobic treatment systems. So it is the crucial for enhancing theefficiency and the stability of anaerobic digesters by strengthening function ofHPAs. While the response characteristics of HPAs to organic loading rate (OLR)and pH was basis to strengthen function of HPAs in digestors.An upflow anaerobic sludge blanket (UASB) reactor and an anaerobic baffledreactor (ABR) were chose. The impact of OLR and pH on performance of reactorswere investigated, respectively. The succession of HPAs was detected bypolymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE).On this basis, the intrinsic link between the HPAs succession and performance ofUASB and ABR was discussed, and then put forward the strategy of strengtheningHPAs. The study will lay the foundation of development high rate anaerobictreatment technology by strengthening HPAs.According to the structure and process characteristics of UASB and ABR, thereactors were started in different ways. UASB was started by fixing influent CODconcentration and phased shortening of hydraulic retention time (HRT).A steadystate was achieved with an influent COD1000mg/L and HRT8h after180dcontinuously running, a COD removal rate of90%was obtained and anaerobicgranular sludge was cultivated successfully. ABR was started at lower OLR, asteady state was obtained with an influent COD8000mg/L, HRT36h and OLR5.4kg COD/m~3·d after228d continuously running, and microbial-phase separationwas achieved in the ABR. The acidogenic phase was formed in the first twocompartments, while the methanogenic phase was formed in the last twocompartments. Thus, microbial-phase separation laid a foundation for performingsteady and pollutant removal effectively in the ABR.Response of HPAs on OLR change was investigated after start-up of UASB and ABR systems. The results showed that HPAs succesion was obvious with OLRincrease in these two bioreactors. Under low OLR condition (<10kg COD/m~3·d),Syntrophobacter wolinii (HPAs) with low specific maximum degradation rate (Umax)and specific maximum growth rate (μ) was the dominant HPAs. With OLR increase,Pelotomaculum propionicicum and P. schinkii with high Umaxand μ was thedominant HPAs in turn. Succession of HPAs inhanced the hydrogen-producingacetogenesis in systems, resulting in treatment efficiency of UASB and ABR wassignificiantly improved with COD removal of above92%during the OLRincreasing. During the wastewater anaerobic biological treatment process, therefore,periodical OLR shocks could promote HPAs succession and improvehydrogen-producing acetogenesis for long-term stable operation of an anaerobicsystem.In UASB, the distribution and dominance of HPAs were significantly affectedby pH reduction. The dominance of Pelotomaculum schinkii in the reactor wasobviously decreased with pH reduction, resulting in COD removal was deceased to68%from90%with propionate1250mg/L. These results indicated that thehydrogen-producing acetogenesis was the rate-limiting step in UASB when pH wasthe restrictive ecological factor. Therefore, not only methanogens should beenhanced but also HPAs should be enhanced during the operation and regulation ofUASB.ABR had a favourable buffer performance to pH reduction. COD removal ofABR was above93%at pH8.0~6.0in influent. A good buffer performance of ABRdepends on the positive response of major functional community on pH reduction.Reduction of influent pH made fermentation type in acidogenic phase was changedand then promoted HPAs succession. In wastewater anaerobic biological treatmentprocess, fermentation type in acidogenic phase could be regulated as ethanol-typefermentation by adjusting influent pH. Ethanol-type permentation would supplyoptimum substrate for HPAs, leading to a high efficiency hydrogen-producingacetogenesis and then improving the performance of anaerobic biological treatmentsystems. In addition, synchronous hygrogen methane-production in ABR would become true if the acidogenic phase was controled as ethanol-type permentation.