Strengthened Coagulation For Advanced Treatment Of Piggery Wastewater And Preparation Of Adsorbent Material From Sludge

Piggery wastewater is a kind of high concentration organic wastewater with high COD and ammonia nitrogen concentration,strong odor,deep chroma,large amount of heavy metals,antibiotics,bacteria and pathogens.The common pig wastewater treatment process is‘Biogas digester+Biochemical treatment+Advanced treatment’.Biochemical treatment discharges excess sludge,and biochemical tail water is difficult to meet the requirements of Discharge standard of pollutants for livestock and poultry breeding（GB18596-2001）.For the increasingly stringent new standards,the effluent effect of traditional processes（such as combined process effluent in summer）is difficult to meet the discharge requirements.At present,there are few studies on the treatment and disposal of excess sludge in pig farms.The general treatment and disposal method is to prepare organic fertilizer by mixing dewatered sludge with manure residue.The excess sludge contains a lot of heavy metals and antibiotics,which will pollute the environment directly.This study includes two parts:（a）advanced treatment of biochemical effluent by coagulation,recovery of on-site coagulation chemical sludge and its application in the preparation of composite materials;and（b）treatment of excess sludge by FeSO₄coagulation-hydrothermal treatment-pyrolysis（CHP）,using the product as adsorbent material for the adsorption of TYL.The following conclusions can be drawn from the experimental research:（1）Na⁺zeolite-Mg²⁺&Fe³⁺chloride double coagulation can better remove COD,TP,NH₄⁺-N and turbidity in pig tail water,which can effectively improve the quality of effluent.The optimum parameters of this coagulation method are as follows:concentration ratio NMZ/NH₄⁺-N=100,molar ratio of iron to phosphorus 2.7,molar ratio of magnesium to iron0.5,which is suitable for tailings with influent p H ranging from 4.5 to 9.5.（2）The main component of adsorbent prepared by pyrolysis based on chemical coagulation sludge is Na⁺modified zeolite,which also contains a small amount of minerals,metal oxides and biochar.It showed perfect adsorption capacity for Cd²⁺in aqueous solution.Langmuir adsorption isotherm（R²=0.998）can well fit the adsorption process better.The Cd²⁺adsorption on composite（sludge pyrolyzed at 500℃）can be well expressed by Langmuir isotherm model with theoretical maximum adsorption capacity of139 mg/g,which is in agreement with the experimental values.The main adsorption mechanism is chemical adsorption,including ion exchange and complexation precipitation.（3）FeSO₄ coagulation was used to treat pig farm excess sludge.After coagulation,SV₃₀ of sludge decreased from 97%to 30%,and water content of sludge decreased from 97%to30%after hydrothermal treatment.After CHP treatment,the residue states of Cd,Pb,Cu,Zn,Cr and Ni increased by 12.1%,67.3%,12.4%,15.4%,58.5%,2.8%respectively.With the increase of Fe²⁺concentration,the proportion of residual state continues to increase.Besides,CHP has excellent ability to immobilize heavy metals of Pb and Cr.CHP treatment can effectively reduce the water content of sludge,and transform the form of heavy metals from acid soluble and reducible forms which are easy to be utilized and migrated by plants to relatively safe and stable oxidizable and residual forms.（4）The composite material prepared from excess sludge by CHP treatment is a kind of composite material composed of goethite,quartz,biochar and polymer.It showed a strong adsorption capacity for TYL.Langmuir adsorption isotherm can well fit the adsorption process（R²=0.947）.The maximum theoretical adsorption capacity of the composite material pyrolyzed at 600℃is 58 mg/g,which has practical value in efficiency.Adsorptive properties include physical adsorption,electrostatic interaction,hydrogen bonding and cation exchange.