Photosynthetic bacteria treatment of synthetic soybean wastewater: Direct degradation of macromolecules

In order to investigate the possibility of photosynthetic bacteria (PSB) to degrade macromolecules directly and to find an economic PSB wastewater treatment method without energy input, a new strain of PSB, Z08, was used to treat synthetic soybean wastewater. Coagulation and yeast were used as pretreatment when needed. Results showed that Z08 directly degraded soybean wastewater under natural conditions without extra light or oxygen supply. After 72 h, COD reduced by 95.7%, macromolecules decreased by 75.4%, meanwhile small molecules (MW < 3000) increased and counted for 79.8% of the products. Main products were C2–C5 acids which contributed 60% of residual COD. There was a COD reduction limit for PSB treatment, and activated sludge was used after PSB; the overall COD removal was 99.4% after 90 h. Z08-activated sludge treatment is economical and simple to realize contaminant reduction and resource utilization.