Investigation And Integrated Application Of Deep-dewatering Technology For Fecal Sludge From Public Toilet In Rural Areas

Non-sewered sanitation has recently been acknowledged as a long-term sustainable solution.Based on this concept,China government has proposed a program to build modern sanitation facilities in rural areas,encouraging the establishment and renovation of decentralized public toilets.The treatment of fecal sludge and sewage could be implemented in decentralized or centralized way according to local conditions.The conditioning technology for sewage sludge has been studied for more than a century,but for fecal sludge it is still in the early stage.The growing production of fecal sludge has also posed a tremendous challenge to FS management and disposal.Therefore,exploration of fecal sludge conditioning technology and corresponding integrated equipment,which is suitable for decentralized public toilets in rural areas,is an important step for promoting rural habitat environment.The conditioning effects and mechanisms of conventional coagulation and advanced oxidation conditioning systems on fecal sludge（FS）were investigated in a systematic study.The optimal operating conditions for each conditioning system were determined by studying the effects of conditioner dosage,contact time,and p H on the dewatering capacity of FS.In addition,on the basis of bench-scale testing,vehicle-mounted mobile integrated FS treatment equipment was developed and implemented for in-situ treatment of decentralized public toilets,achieving favorable and stable processing outcomes.Finally,a brief analysis of the equipment’s operating expenses was provided.In FS conditioning experiments with various conditioners（Fe Cl₃,PAC and PAM）,PAC and PAM were observed to be more effective treatments than other conditioners.Due to the sludge-water separation caused by the flocculation effect,it was possible to obtain a stable conditioning effect in a relatively short contact time（3-5min）with the use of these two conditioners.In a subsequent step,PAC alone,PAM alone,and the combined PAC/PAM system were used to condition various sources of FS（water latrines,dry latrines and large trench latrines）.PAM was determined to be the optimal conditioning method for local FS dewatering treatment due to its superior conditioning effect when compared to the other two conditioning methods.It could simultaneously remove organic contaminants and nutrients from the FS supernatant while reducing the dewatering time and water content of the FS press cake.Zero-valent iron-activated persulfate（ZVI/PDS）oxidation system was applied to the FS conditioning process in order to effectively enhance the FS dewatering properties.Positive correlations were observed between ZVI and PDS dosing,contact time,and the dewatering capacity of FS,whereas the effect of p H on the ZVI/PDS conditioning process was relatively complex,as acid and base not only altered the dewatering performance of FS directly,but also acted on the dissolution process of iron ions,which further influenced the conditioning effect of the system.The CST on FS was reduced by 97.3±0.3%under the conditions specified.In addition,the ZVI/PDS system was effective at removing and transferring pollutants from the FS supernatant,as evidenced by the reduction of COD and TP by 60%and 94%,respectively.The mechanism study revealed that SO₄·^-and·OH radicals could be generated simultaneously in the ZVI/PDS system,which could effectively degrade EPS components（proteins,polysaccharides,etc.）in FS and oxidize hydrophilic functional groups on the surface of fecal sludge particles.This process decreased the hydrophilicity of the surface of FS particles,which,in conjunction with the coagulation effect produced by multivalent iron ions,promoted their flocculation and sedimentation.After treatment with the ZVI/PDS system,FS was found to have a lower zeta potential,larger flocs,and lower viscosity,which indicates a significant improvement in FS dewatering performance.The dewatering-drying linkage test and on-site treatment were applied to FS selected at random from decentralized rural public toilets.The results of the simulated linkage test indicated that the dewatering and drying processes could reduce the water content of fecal sludge to 78-85%and 16-38%,respectively.The ehicle-mounted mobile integrated FS treatment equipment has a continuous and stable treatment capacity with the ability to pump,dewater,and dry FS on-site.Treatment with this equipment resulted in a significant reduction in water content（30-40%）and removal of COD&TP（97%）by FS,despite the minor variations in TN and NH₃-N concentrations.According to operational records,the average unit treatment capacity of the equipment is 0.52 m³/h,and its unit treatment cost,excluding labor,is 19 RMB/m³,which is considered to be a reasonable amount.