Performance Of Zeolite Trickling Filter And Multi-soil-layering System Combined Two-stage System For Treatment Of Decentralized Domestic Wastewater

As for general rural area and small towns in China, the decentralized treatmentmode for domestic wastewater is the most applicable alternative, as the modecharacterizes in treatment on-site and reuse on-site, avoids network construction,and reduces specialized managements.A novel two-stage treatment system was developed based on decentralizedtreatment requirements. The treatment system consisted of Zeolite trickling filter(ZTF) as the former stage and Multi-soil-layering system (MSL) as the second stage.The trickling filter was packed with coarse zeolite segregated thin iron scraps layers,referred to as the Iron modified Zeolite Trickling Filter (IZTF). The main characterthe IZTF acted as was the pretreatment facility for partial removal of SS, organicmatters and ammonium in septic effluent. The MSL makes use of soil by packing thesoil blocks into zeolite filler, thus creates complex ecological conditions formicrobial populations and treats wastewater in depth.Long-term performance of IZTF, ZTF, and MSL as well as the compoundIZTF-MSL system was investigated and the main conclusions are as follows:1. The stability of the performance of upper layers of MSL was not so good asthat of traditional bio-filter when the permeable filler was natural zeolite. As thepretreatment facility, it is suggested to use bio-filter reactor that was packed withhomogeneous materials, which, as a result, helps the efficient and stableperformance of the system.2. The intermittent influent mode, the coarse zeolite filler and the structure ofIZTF with low packing height contributed the oxygen supplement of the reactor,enhanced the removal of organic pollutants, ammonium and SS, which did notexhibited lack of oxygen even when influent organic loading rate and ammoniumloading rate reached300g CODCr·m-2·d-1and40g NH3-N·m-2·d-1, respectively. Thefluctuation of influent had little influence on nitrification intensity of the reactor.3. Remarkable simultaneous denitrification process was observed in IZTF aswastewater rich in organic matters was fed into the reactor directly. However,denitrification intensity in the MSL was weak during the study as its influent lackedcarbon resources, thus the removal rate of TN was low and effluent TN exceeded20mg·L-1. The results of partial effluent determination (TN and pH analysis) provedthe Soil mixture blocks packed in the MSL significantly enhanced the denitrification process.4. The thin iron layer packed in the zeolite filter reactor remarkably enhancedits TP removal, which was higher and more stable compared with MSL with identicalpacking height and iron mass percentage.5. Total removal rates of CODCr, TP, Ammonium, and TN ranged90.3%~95.2%,92.0%~94.0%,85.1%~86.9%, and58.9%~63.8%, respectively at mean hydraulicloading rate of920L·m-2·d-1and under relatively stable conditions and effluentwater quality reached class one A standard in "National Discharge Standard forWastewater Treatment Plants of cities and towns"(GB18918-2002) except for TN.6. The two-stage structure ensured the stability of the performance and thewellbeing of effluent quality as majority pollutant was entrapped in the former stage.no ponding, clogging or channeling happened during the operation of the apparatus.No artificial aeration was needed and the requirement was little, making the facilityappeal to the decentralized sewage treatment very much.