The potential use of purple nonsulfur bacteria to simultaneously treat chicken slaughterhouse wastewater and obtain valuable plant growth promoting effluent and their biomass for agricultural application

Abstract

Abstract Treatment of wastewater with purple nonsulfur bacteria (PNSB) simultaneously produces the biomass of plant growth promoting bacteria (PGPB) and the effluent containing plant growth promoting substances (PGPS). Among 46 PNSB strains isolated from chicken slaughterhouse wastewater (CSW) treatment unit, only four strains grew well in non-sterile effluent of the anaerobic digester (CSW-Di), under both microaerobic light and aerobic dark conditions. However, only strains WS308 and WS502 were selected as inoculants for subsequent experiments since they released high levels of 5-aminolevulinic acid (ALA) into the digester effluent medium under both incubating conditions. Based on 16S rRNA genes analysis, the strains WS308 and WS502 were identified as Rhodopseudomonas faecalis and Rhodopseudomonas palustris, respectively. The central composite design (CCD) experiments were conducted by using a mixed culture of the two strains (1:1) treating the non-sterile CSW-Di (soluble chemical oxygen demand, sCOD 736 mg/L) under 72-hr microaerobic light condition. The optimal conditions on the multivariate regression were found at the inoculum size (X1) of 3.63% (roughly 106 cells/mL), initial pH (X2) of 6.9 and light intensity (X3) of 3731 lux. At this condition, sCOD removal was predicted at 85.3%, while the verification test result favorably achieved 88.1% removal. ALA concentration in CSW-Di of the verification set was found at 0.13 mg/L. All trace elements detected in CSW-Di effluent were much lower than recommended maximum concentrations for irrigation water. Treating wastewater with potent PNSB strains could produce effluent containing PGPS, such as ALA, and also the biomass as PGPB for organic agricultural applications.