Experimental Study On Enhanced Coagulation Of HCA And Its Compound Coagulant For Pretreatment Of Domestic Sewage In Northwest China

With the continuous promotion of the pace of economic construction in the new rural areas,the rural environmental construction has been gradually paid attention to,especially the treatment of rural domestic sewage.Due to the limitation of low temperature period,unstable water quality and economic conditions in northern China,the treatment of domestic sewage is poor,the treatment is difficult and the cost of treatment is high.In view of the existing problems in domestic sewage in the north of China,the experimental study on the enhanced coagulation pre treatment of rural sewage with poly(two methyl diallyl ammonium chloride)(HCA)as the main coagulant and HCA and its compound coagulant is carried out to reduce the processing load of the subsequent treatment unit and reduce the cost of infrastructure.The goal of economic and effective prevention and treatment of domestic sewage in Northwest China is achieved.The main factors of HCA single factor test are: hydraulic conditions(mixing agitation,flocculation agitation intensity and time),initial p H value,HCA dosage and SS,TP and COD removal rate as evaluation indexes,combining fractal dimension and Zeta potential test results to verify the effect of HCA processing,and the parameter values of each factor are as follows:in water The mixing stirring speed of 400r/min,mixing stirring time 1.5min,flocculation stirring speed 100r/min,flocculation stirring time 5min,initial p H value 8.5-9.0,HCA dosage15mg/L,HCA SS,TP and removal rates can be up to 92.2%,74.9%,65.1% respectively at this time in the range of 15 C-23 C.When the addition of HCA is 15mg/L,the fractal dimension and Zeta potential are 1.0149 and-2.03 mv respectively,which conforms to the fractal dimension and the characterization of Zeta potential,and further illustrates the rationality of the experimental screening results and the applicability of the two methods.In order to further optimize the parameters of HCA coagulation,orthogonal test was carried out on the basis of single factor test.The main factors were as follows: initial p H value,HCA dosage,mixed mixing speed gradient,mixed mixing speed gradient,mixed stirring time,flocculation agitation speed gradient and flocculation agitation time.The results showed that the effects of various factors on the effect of HCA were as follows: initial p H value >HCA dosage > mixed stirring speed gradient > mixed stirring time > flocculating agitation speed gradient > flocculating stirring time.The results of Zeta potential and fractal dimension show that the fractal dimension of the floc with good treatment effect is larger and the absolute value of Zeta potential is closer to the 0m V point.The orthogonal test optimized the coagulating conditions of HCA separately: mixed mixing G value of 244.3-268.2s-1(<15 C),mixed mixing GT value 7329-8046,flocculation G value 38.9-40.5s-1,flocculation time 5min,initial p H 8.5-9.0,HCA dosage is 15mg/L.On the basis of the analysis of the orthogonal test results,the coagulation mechanism of HCA treatment of domestic sewage was preliminarily studied.The results showed that in the process of coagulation,HCA mainly played the characteristics of high positive charge,formed tiny wool flocs through electric neutralization,and then gradually made fine flocs gradually by adsorption bridge and net capture and scanning.Condensation is the final settlement of larger floc particles,so as to achieve the purpose of removing pollutants from water.In order to further explore the treatment effect of HCA compound coagulant,the compound test between HCA and inorganic coagulant(Fe Cl3,PAC,PAFC)and organic coagulant(PAM,AM)was carried out,and the effects of adding ratio,initial p H value and dosage factors on the treatment effect of the compound coagulant were mainly investigated.Through the comparison of the combination treatment effect of HCA and other coagulants,when the HCA:PAC dosage is 1:20,the dosage is 10mg/L,the initial p H value is about 8.5,the SS removal rate is above 90%,the TP removal rate is about 65%,the COD removal rate is about 60%,and the floc particles are relatively coarse compared with those of the other compound combinations.It is very stable,and the amount of investment is relatively small.In this paper,the influence of temperature on the effect of HCA treatment was investigated in the northwest area.The effect of temperature on the effect of HCA treatment was investigated,and the effect of HCA treatment under the normal temperature and low temperature(below 15 C)was compared.The results showed that the temperature had little effect on the HCA treatment effect.Although the evaluation indexes increased at lower temperature,the increase range was less than 10% at room temperature.At the end of the paper,using the software Design Expert8.0,the main parameter values of the factors affecting the effect of HCA treatment of domestic sewage were optimized according to the Box-Behnken Design(BBD)experimental design.The evaluation index of SS,TP and COD removal rate was still used during the process.The results showed that the flocculation time of the orthogonal test was 5min,and the initial p H was about 8.5.The adding amount of HCA is 15mg/L,the initial p H value obtained by the response surface method is close to the orthogonal test results.The flocculation stirring time is basically near5 min,but the optimization value of HCA dosage is different from the orthogonal test value,and the removal rate of SS,TP and COD is 90.2%,25.7% and 39.9% respectively.