Technical Study On Cassava Starch Wastewater Treatment Of Mixed-culture Fermentation And Production Of Single Cell Protein

With the increasing demand for cassava products and the rapid development of cassava processing industry, cassava processing industry stimulates the local economic development but also brings a certain degree of environmental pollution at the same time. Cassava starch wastewater comeing from cassava starch production process is the major pollution of the cassava processing industry currently. Cassava starch wastewater’s treatment is very difficult, because of its characteristics of high suspended solids concentration, high organic pollutants concentration, low pH and large load changes (water quality and quantity changes), together with the discontinuity of cassava starch wastewater’s producing. Currently, most starch factories are using traditional biochemical methods to process cassava starch wastewater, and the disposal results are often not good enough according to the emission standards; few facturies process wastewater with advanced technique which achieve better disposal effect, but the resource utilization is not adopted in these wastewater disposal process, which results in resources waste.This study applied aerobic biological method on cassava starch wastewater treatment, and single cell protein (SCP) was produced by mixed-culture fermentation through the microbial synergies at the same time. The study was carried on by correcting of microwave digestion method, characterizing of cassava starch wastewater, screening for strains with high amylase and cellulase production ability, screening for strains with high SCP production ability, optimizing conditions on single-strain fermentation, optimizing conditions on mixed-culture fermentation, and determining the optimal fermentation technique by orthogonal test. It showed that diposal method in the study could improve the microbia’s degradation ability for organic pollutant in cassava starch wastewater, which help cleaning wastewater more efficiently, secondly, the method could improve production of SCP which coulld be collected and used as feeding-protein, then the aim of wastewater resources utilization was achieved. The experimental results indicated that:(1) The CODcr outcome of microwave airtight fast digestion method approached mostly to the method of potassium dichromate reflux under the condition of:the amounts of waste water samples was4mL, the amounts of masking agent was1g/L, and the microwave digestion cans was put around the outer circle of the template.(2)The pH of cassava starch wastewater3.80～4.30, it contains1.11g/L～1.23g/L protein and0.62g/L～0.66g/L reducing sugar,8.01g/L soluble solid content, the CODcr and BOD5in the waste water are12744.7mg/L and7896.6mg/L separately。(3) It is showed that Aspergillus niger is suitable strain for starch and cellulose degradation by tracking and analysing the reducing sugar content, and Candida tropicalis is suitable strain for SCP production by analysing the protein content.(4) The single factor experiments show that the optimal conditions in mix culture fermentation as follow:6%inoculating quantity,130mL medium, inoculation for20h, initial fermentation pH at5, culture temperature at29℃and rotation at175rpm。(5) The removal rate of CODcr is96.2%with16.16g/L SCP harvest under the condition:8%inoculating quantity,130mL medium, inoculating yeast20h after A. niger’s inoculation, initial pH4.5, culture temperature at29℃, rotation at200rpm.