Effect Of Peanut Shell Biochar And Tween 80 Addition On Municipal Sludge Composting

With the continuous development of our society,the annual output of sludge in China has gradually increased.It is estimated that the output will reach 6.0×107 tons by 2020.How to effectively solve the problem of sludge pollution has become the focus of current attention.The sludge is rich in a large amount of elements such as nitrogen,phosphorus and potassium.Therefore,the use of municipal sludge for composting has become a research hotspot in recent years.However,municipal sludge also contains a large amount of toxic heavy metals,which also creates technical obstacles for the composting of sludge.Today,composting technology has the function of passivating heavy metals,but the passivation rate is not high.Therefore,it is a new research hotspot of composting to study the addition of various conditioning agents to improve the composting passivation rate.However,focusing on heavy metal passivation may neglect the nutrient of compost products and limit the application of compost products.Therefore,it is of great significance to seek a conditioning agent that can not only effectively improve the passivation effect of heavy metals but also maintain the nutrient of compost.The effect of peanut shell biochar(PB),Modified peanut shell biochar(MPB)and Tween 80(TW)addition on thermophilic compost of sewage sludge(SS)with wheat straw was investigated.Six treatments were designed with PBO%(CK),PB5%(DH),MPB5%(DG),TW0.2%(DT),PB5%+TW0.2%(DHT),MPB5%+TW0.2%(DGT).The temperature,moisture content,pH value,electrical conductivity(EC),ammonium nitrogen(NH4+-N),nitrate nitrogen(NO3'-N),total phosphorus(TP),available phosphorous(AP),total potassium(TK),the total Cu,Zn,Mn and the different speciation of Cu,Zn and Mn were determined.Comparing the multi-faceted effects of the three conditioners on composting and the combined application effect,the best composting agent combination was obtained.Comparing the multi-faceted effects of the three conditioners on composting and the combined application effect,the best composting agent combination was obtained.The conclusion is as follows:1)Adding PB and MPB can effectively increase the pH value of the heap,However,the addition of TW has little effect on the pH of the heap.For the value of EC,the addition of PB and MPB can increase the it,but TW has little effect on it.2)The concentrations of NH4+-N,NO3--N,TP,AP,TK and AK increased after composting in CK,DH and DG treatments.Among them,the relative change rate of NH4+-N mass fraction in the CK is 31.75%.The relative change rates of NO3--N,TP,AP,TK and Ak in the DG test group were the highest,which were 59.81%,28.82%,32.28%,14.75%and 24.59%,respectively.The concentrations of NH4+-N,NO3--N,TP,AP,TK and AK increased after composting in DT,DHT and DGT treatments.Among them,the relative change rate of NH4+-N mass fraction in the DT test group is 39.65%.The relative change rates of NO3--N,TP,AP,TK and AK in the DGT were the highest,which were 64.47%,73.44%,51.07%,16.86%and 32.27%,respectively.This results indicated that,compared with CK treatment,the treatments of DHT and DGT are beneficial to promote the improvement of compost nutrient,especially for the improvement of TP.3)The total Cu and total Zn mass fractions of the CK,DH and DG without Tween 80 increased,and the total Mn mass fraction decreased.Among them,the relative change of total Cu and total Zn mass fraction in the DH test group was 97.22%and 23.96%,respectively;the relative change rate of total Mn mass fraction in the CK test group was-17.62%.In DT,DHT and DGT treatments,the concentrations of total Cu increased and total Zn and total Mn decreased.Among them,the relative change rate of total Cu mass fraction in DHT test group was 41.68%,and the relative change rate of total Zn and total Mn mass fraction in DT test group was the highest,which was-49.51%and-13.92%,respectively.This results indicated that compared with CK treatment,the treatments of DH and DG are beneficial to promote the improvement of total Cu,total Zn and total Mn.However,the treatments of DHT and DGT are beneficial to decrease the relative change rates of total Cu,total Zn and total Mn.4)In the CK,DH and DG test groups without Tween 80,the Cu passivation rate of the DG test group was 37.16%;the Zn passivation rate of the DH test group was 25.38%;the DG test group had the highest Mn passivation rate.It is 24.62%.In the DT,DHT and DGT test groups with Tween 80 added,the Cu passivation rate of the DGT test group was 55.01%;the Zn passivation rate of the DHT test group was 36.52%;the maximum Mn passivation rate of the DGT test group was 32.54%.This results indicated that the treatments of DHT and DGT are most powerful to the passivation of heavy metals,especially for the heavy metals of Cu.It can conclude that PB,MPB and TW has a positive effect for the improvement of composting nutrients and passviation of heavy metals,above all,the DGT treatment works.