Study On A Quick Treatment Technique Of Swine Wastewater By Using Biological Coagulation Followed By SBR Process Or Constructed Wetland

In 2015,the amount of pig slaughter and livestock on hand had reached 708 million and 451 million nationwide,and the proportion of large-scale pig farms whose amount of pig slaughter was over 500 had been up to 41.8%in 2014.It could provide a great number of livestock and poultry products.In the meantime,it brought a problem of a large amount of swine wastewater which needed to be treated.This kind of wastewater,characterized by large quantities of discharge and high pollution load(high concentration of COD,NH3-N and TP),contaminates the surface and underground water,atmosphere and soil if been discharged into water body.As a result,it can do harm to human and animal health.In recent years,a large number of domestic and foreign researchers and actual projects have done a lot to enhance the effect of swine wastewater treatment.The methods for swine wastewater treatment mainly include physicochemical techniques(flocculation and precipitation,adsorption and ion exchange treatment),biological techniques(aerobic,anaerobic and anaerobic-aerobic treatment)and natural treatment(constructed wetland and oxidation pond treatment).However,the effect of swine wastewater treatment is still unsatisfactory at present.It's very hard to meet the water quality standard regulated by China when treatment technique is applied alone.But it still has the weaknesses of long processing flow and period,high cost and extra carbon source and alkalinity when treatment techniques are applied together.Thus,it is still an urgent and difficult task to advance and develop techniques,which is based on figuring out the problems and causes of present treatment techniques for swine wastewater.Therefore,these key issues were systematically studied in this paper and the main conclusions were as follows:(1)The effluent from a large-scale pig farm and achieved by solid-liquid separator still contained high concentration of SS,COD,NH3-N,TN and TP,and the highest concentration reached 11 290,1 044 and 55.5?148.1 mg·L-1.And the conventional anaerobic digestion process mainly removed soluble COD for a short time.As a result,the biodegradability of biogas slurry became worse.Consequently,the effluent from the secondary clarifier still contained 37.9?108.7 mg·L-1 NH3-N,179.1?203.4 mg·L-1 TN,and 20.1?41.6 mg·L-1 TP,which couldn't meet the water quality standard.Therefore,additional two CASS tanks had to be constructed to continuously treat the effluent from the secondary clarifier.However,TP concentration of the effluent by CASS process still couldn't meet the water quality standard,and the effluent was of high chroma.Obviously,it was still very difficult for conventional biological treatment technique to treat the large-scale swine wastewater to completely meet water quality standard.(2)High concentration of SS and "inert" COD,N,and P were found to be responsible for the phenomenon.Therefore,to develop a new technique with completely removal of SS in the first stage followed by conventional secondary biological treatment was expected to enhance the effectiveness of large-scale swine wastewater treatment plant.(3)The sedimentation rate of swine slurry with biological coagulation sedimentation treatment was better than chemical flocculant treatment.And the process could remove nearly all SS and a substantial part of N and P at the same time.The specific resistance to filtration of concentrated swine slurry after biological coagulation reaction decreased to(0.3?0.5)×1012 m·kg-1,which indicated its dewaterability was improved significantly.And the moisture content of semi-drying slurry cake from biological coagulation treatment was decreased to 56.49%.The concentration of SS,COD and TP in filter pressing water had met the water quality standard,which could achieve the level of secondary biological treatment.The effluent of 24 h SBR process for filter pressing water could completely meet water quality standard,which shorten the treatment process and period when it was compared to the original treatment technique.(4)The effect of MSL model constructed wetland for simulated and actual swine wastewater treatment was better than conventional vertical subsurface flow constructed wetland.The removal of reductive materials(iron filings and sawdust)in MSL model constructed wetland had a significant influence on treatment effect.The MSL model constructed wetland without reductive materials had the best and most stable treatment effect,of which the concentration of COD,NH3?N,TN and TP in the effluent was 80?100,70?85,80?110 and 0.3?1.0 mg·L-1,respectively.And the removal rate was 85%,45%?50%,35%?55%and 90%?98%accordingly during later running period.The treatment effect of swine wastewater was satisfactory by using biological coagulation followed by MSL model constructed wetland without reductive materials,of which the total removal rate of COD,NH3-N and TP was 92.77%?70.15%and 98.04%.Therefore,the biological coagulation process followed by SBR process and constructed wetland,which can recycle SS and "inert" contaminants efficiently at the first stage,ean not only shorten treatment process and period,but also recycle nutrients in wastewater,when it is used to treat large-scale and small-scale swine wastewater,respectively.Consequently,it can enhance treatment effectiveness and reduce the costs.The results of this study can provide basis and reference for engineering staff who are engaged in similar wastewater treatment field and farm owner to advance and optimize present treatment techniques.