Studyof Combined Pretreatment-UASB-A/O-BAF Process In Soybean Protein Wastewater Treatment

Soybean protein is plant-based protein, containing8kinds of amino acids,which is almost the same with the recommendation of FAO and WHO. It can be equivalent to animal protein on the nutritional value, the genetic structure of amino acid is most close to the human body, so it is one of the most nutritious plant protein. According to statistics, more than10million tons was used for domestic soybean food processing industries in2012, of which about30%was used in the production of the soybean protein, the annual output was more than70thousand tons. Soy protein processing in our country is developing rapidly, exports accounted for more than50%of the total volume of soybean protein in the world.Soybean protein wastewater (SPW) is produced during the soybean protein processing which mainly includes alkali-solution, acid-isolation, centrifugal process. The centrifugal produces large amounts of whey wastewater, is the main link of pollution sources. This kind of wastewater has the following characteristics:(1)SPW is shown ivory, has high content of organic matter, such as polysaccharide, protein, fatty acids, at the same time, a certain amount of inorganic salts and tiny suspended solids is also contained. The molecular mass of SPW is whey protein2000-20000Dt and oligosaccharide300-700Dt.(2)The other characteristics of SPW are low acidity, high temperature, and great variation is often observed in either composition or flow rate. BODs/CODCr of SPW is higher than0.35.(3) The main water quality indicators of SPW:CODCr:1200023000mg/L,BOD5:6000～12000mg/L,SS:2200～7350mg/L,total nitrogen:670-1000mg/L,pH:4～5, temperature:50-60℃。 Base on consult a great deal of literature and datum and research of Sewage treatment in three Soybean protein production manufacturers.This study adopted combined pretreatment-UASB-Two stage A/O-BAF process to treat SPW.The research included two parts:the experiment and practical application.Firstly, the experiment part:1.In order to reduce organic loading of the subsequent bio-treatments, cavitation-pocket flotation+dissolved air flotation were used for pretreatment in pilot scale experiment (500L/h);2.UASB reactor,which was inoculate by urban sludge,and two stage A/O were selected for the biological treatment in lab-scale test (187.5L/h);3. In order to achieve discharge standard, chose BAF for advanced wastewater treatment in lab-scale test. Secondly, combined pretreatment-UASB-Two stage A/O-BAF process was applied in the practical wastewater treatment of soybean protein production factory. The main conclusions were summarized as follows:1.SPW contains high amount of organic matters,and BODs/CODcr of SPW is higher than0.35. Therefore, biological technology is suitable for SPW treatment. Based on comprehensive analysis of numerous literatures, biological treatment technology mainly composed of UASB and A/O was adopted in SPW treatment.2. Cavitation-pocket flotation and dissolved air flotation could remove most of SS in pretreatment. The effluent SS was1200mg/L,while the influent was4000-5000mg/L.Tt reduced this influence of high SS to anaerobic treatment.3. Well performing granular sludge was cultivated by inoculation with urban sludge in UASB. UASB achieved good processing effect with volume load of6.8kgCODCr/(m3·d), CODCr removal rate of90%.4.Both of CODcr and NH3-N removal rate was higher than90%in two stage A/O for aerobic treatment. 5.Part of ammonia was converted to nitrite nitrogen, and nitrite nitrogen would influence effluent CODcr,if denitrification was not complete.Through the research of principle and experiment, this study verified the theory of the influence of nitrite nitrogen for CODcr·6.The result of BAF experiment showed that it was feasible to use BAF for advanced treatment of SPW. The optimum conditions were media height of80cm, HRT of4h, and A/L of15:1, meanwhile, water quality discharged were CODcr^60mg/L, BOD5≤20mg/L, ammonia nitrogen≤5mg/L, SS≤20mg/L, chromaticity≤30.7. The systerm of pretreatment-UASB-two stage A/O-BAF process worded well in practical application, the indicators of effluent was lower than the limits of the discharge standards of Shandong Province (CODcr≤60mg/L, BOD5≤20mg/L, ammonia nitrogen≤5mg/L, SS≤20mg/L,chromaticity≤30).8.The results of both experiments and practical application of pretreatment-UASB-two stage A/O-BAF indicated the technology achieved very good processing effect with Low cost.Tt could provide guidance for the theory and practice of SPW treatment.