Study On The Pre-Treatment Of Sweet Potato Starch Wastewater By Chitosan Modified Clay Compounded With Polyglutamic Acid

Starch,as an important product in human life,is used more and more widely.The high organic concentration of wastewater generated in starch processing will cause serious pollution.The sweet potato starch production in China has large scale and is mainly concentrated in rural areas causing the wastewater an urgent environmental problem.Conventional biochemical treatment is hard to take effective performance due to the sesonality flutuation of sweet potato starch production that concentrated in winter time from October to December.There is an urgent need in developing efficient and low-cost physicochemical treatment for rural sweet potato starch wastewater.In this paper,the chitosan-modified clay composite polyglutamic acid treatment was studied for this wastewater,and the effective performance was achieved.The main research contents and conclusions are as follows:(1)The simulated sweet potato starch wastewater was prepared as object.Water quality and its change in the hydrolysis and acidification process was analyzed systematically.The study found that the concentration of organic pollutants is high,with COD of 8179 mg / L,total nitrogen of 168.7 mg / L,and total phosphorus of 63.5 mg / L.The turbidity is also at a high level,up to 2200 NTU.The particle size distribution is between 0.2 μm and 65 μm,and the specific gravity of the particulate with a particle size of about 5.44 μm is the highest.Zeta potential analysis found that the isoelectric point(p I value)of starch wastewater is about p H = 4.According to the research on wastewater grading treatment,the particulate total nitrogen in the sweet potato starch wastewater accounted for 40.66%,and the particulate total phosphorus accounted for 28.96%,indicating a dissolved state of both nitrogen and phosphorus.Kjeldahl nitrogen and dissolved organic phosphorus are the main forms.During the 48-hour hydrolysis and acidification process,the pH value of starch wastewater decreased sharply from 6.42 to 3.50;the concentration of NH3-N increased intensely from 6.3 mg / L to 19.3 mg / L;the turbidity decreased from 1649 NTU to 1009 NTU.On the contrast,the concentrations of COD,TN,and TP remained relatively stable,with small changes.(2)Using chitosan and polyglutamic acid as flocculants to treat starch wastewater,the flocculation mechanism and the synergistic effect of chitosan and polyglutamic acid were studied systematically.The study found that the removal rate of turbidity by cationic chitosan can reach 90.5%,and its flocculation mechanism is mainly electric neutralization;the removal rate of polyglutamic acid can reach 91.8%,its flocculation mechanism is mainly bridging;The synergistic pattern of dosing chitosan first is the most effective one,with the highest removal rate and the wildest effective p H range.The turbidity removal rate can reach 98.32%,and the COD,TN and TP removal rates can reach 44.79%,53.44% and 28.09% respectively.After chitosan-polyglutamic acid composite flocculation treatment,the COD,TN,TP and turbidity concentrations of starch wastewater were reduced to 4514.9 mg / L,78.6 mg / L,45.7 mg / L and 34.5 NTU.(3)The tail water(supernatant)treated by chitosan-polyglutamic acid composite flocculation was used as the object.Four typical clay minerals,kaolin,bentonite,zeolite and attapulgite,were selected as adsorbents and systematically studied their adsorption to soluble pollutants in starch tail water.The study found that among these four typical clay minerals,bentonite performed the best in removal COD,TN and TP,with removal rates of 56.3%,48.2% and 28.1%;The concentrations of COD,TN and TP in the treated water were 1871.2 mg / L,39.3 mg / L and 25.1 mg / L,respectively.(4)On the basis of the above research,the chitosan modified bentonite composite with polyglutamic acid,a combination of flocculation-adsorption treatment of sweet potato starch wastewater was studied in order to achieve the optimal treatment effect.The study found that when the mass ratio of chitosan: bentonite was 1: 5,the modified clay had the best treatment effect.After composite treatment,the COD,TN,TP and turbidity concentrations were reduced to 1107.8 mg / L,33.6 mg / L,27.8 mg / L and 40.3 NTU,respectively,and their removal rates were 86.2%,80.3%,52.3% and 98%,respectively.