Biohydrogen production from chemical wastewater treatment in biofilm configured reactor operated in periodic discontinuous batch mode by selectively enriched anaerobic mixed consortia

S Venkata Mohan, Y Vijaya Bhaskar, P N Sarma
Water Research 2007, 41 (12): 2652-64
Molecular hydrogen (H(2)) production with simultaneous wastewater treatment was studied in biofilm configured periodic discontinuous/sequencing batch reactor using chemical wastewater as substrate. Anaerobic mixed consortia was sequentially pretreated with repeated heat-shock (100 degrees C; 2 h) and acid (pH-3.0; 24 h) treatment procedures to selectively enrich the H(2) producing mixed consortia prior to inoculation of the reactor. The bioreactor was operated at mesophilic (room) temperature (28+/-2 degrees C) under acidophilic conditions with a total cycle period of 24 h consisting of FILL (15 min), REACT (23 h), SETTLE (30 min) and DECANT (15 min) phases. Reactor was initially operated with synthetic wastewater (SW) at OLR of 4.8 kg COD/m(3)-day and subsequently operated using composite chemical wastewater (CW) at OLR of 5.6 kg COD/m(3)-day by adjusting pH to 6.0 prior to feeding to inhibit the methanogenic activity. H(2) evolution rate differed significantly with the nature of wastewater used as substrate [SW--volumetric H(2) production rate--12.89 mmol H(2)/m(3)-min and specific H(2) production rate--0.0084 mmol H(2)/min-g COD(L) (0.026 mmol H(2)/min-g COD(R)); CW--volumetric H(2) production rate--6.076 mmol H(2)/m(3)-min and specific H(2) production rate--0.0089 mmol H(2)/min-g COD(L) (0.033 mmol H(2)/min-g COD(R))]. Relatively rapid progress towards higher H(2) yield (2 h) was observed with SW compared to the CW (10 h). Substrate (COD) reduction of 32.4% (substrate degradation rate (SDR)--1.55 kg COD/m(3)-day) and 26.7% (SDR-1.49 kg COD/m(3)-day) was observed with SW and CW, respectively. The system showed rapid stabilization tendency (SW--37 days; CW--40 days) with respect to H(2) generation and COD reduction. H(2) evolution showed relatively good correlation with VFA concentration in the case of SW (R(2)-0.961) compared to CW (R(2)-0.912). A surge in pH values from 5.87 to 4.23 (SW) and 5.93 to 4.62 (CW) was observed during the cycle operation. Integration of biofilm configuration with periodic discontinuous batch operation under the defined operating conditions showed potential to influence the microbial system by selectively enriching the specific group of microflora capable of producing H(2).

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