The Production Of Microbial Fertilizer Using Cassava Ethanol Wastewater

Cassava ethanol wastewater that contains high concentration of chemical oxygen demand(COD)is difficult to treat to meet the discharge standard.However,this wastewater can be potentially materialized as microbial fertilizer by inoculating and growing suitable microorganisms at the expense of the high concentration nutrients.This technology can provide a viable basis for the materialization of wastewater,but also reduce the wastewater treatment costs and thus lessen the environmental pollution.Paenibacillus(P.)polymyxa has the dual role of biocontrol and growth promoting bacteria,which has been applied to agricultural production.This study is mainly on the optimization of wastewater for P.polymyxa using cassava ethanol wastewater for application.This study first explored the optimal growing conditions,including wastewater concentration,temperature,pH and inoculation amount,for P.polymyxa inoculated with cassava ethanol wastewater.The results showed that the wastewater concentration,temperature and pH were the key factors.Based on the results of single factor experiments,the central composite design(CCD)was then used to optimize subsequent experimental conditions.Thus the optimum process conditions were obtained.The P.polymyxa biofertilizer produced from cassava ethanol wastewater was subsequently applied to the vegetables and tomato seedlings to investigate the growth-promoting effects.This research provides a basis for agricultural application and theoretical research of P.polymyxa.The main research results were as follows:1)The optimized condition was containing 61% of cassava ethanol wastewater(COD16 200 mg/L)and 2% inoculum of P.polymyxa,with initial pH at 7.67 and temperature at 38.7°C.A maximum biomass of 1.34×109 cfu/mL was achieved,which was basically consistent with the model-predicted value of 1.33×109 cfu/m L.This microbial inoculum has successfully met the national standard of agricultural microbial fertilizer(≥2×108 cfu/mL,GB 20287-2006),which indicated that it was feasible to produce the microbial fertilizer by growing P.polymyxa at the expense of the cassava ethanol wastewater.2)The growth of tomato seedlings was significantly enhanced with the application of P.polymyxa biofertilizer with the cell concentrations of 1.0×108 cfu/mL,1.0×107 cfu/m L and 1.0×106 cfu/mL.At the optimal concentration of 1.6×108 cfu/m L,the biofertilizer increased the content of fresh weight,dry weight,stem diameter and underground dry weight of tomato seedlings by 60.5%,54.1%,54.1%,22.1%,59.8% and 58.3%,respectively.3)The quality of experimented vegetables was also significantly enhanced with the optimal application of P.polymyxa biofertilizer at the concentration of 3.0×107 cfu/mL.Under this condition,there was a dramatic increment of the fresh weight,dry weight,plant height and vitamin C of vegetables by 69.7%,19.1%,8.9% and 29.2%,respectively,comparing with the negative controls.The liquid P.polymyxa biofertilizer can significantly reduce the nitrate content in the experimented vegetables,which can partically replace the application of chemical fertilizers such as urea,and thus can reduce the biological enrichment of nitrogen induced by excessive usage of urea.