Studies On The Performance Of Vermifiltration For Sewage Treatment And The Physiological Adaptation Of Earthworm In The System

As an environment-friendly sewage treatment technology, vermifiltration hasimmense development prospects in the field of small towns and rural sewage, sludgetreatment. This study provided the design of two-stage vermifiltration to improve thesewage treatment effect. This paper studied the operating results and influencingfactors of filters, and the impact of different temperatures and hydraulic loading onthe filter operating via the actual sewage treatment experiment. A comprehensiveresearch on the performace of vermifiltration was carried through the study ofearthworm physiological adaptation, in order to find the hydraulic load range whereearthworms could play normal ecological functions. It will provide a reference forwide application of vermifiltration popularity.The conclusions illustrated as follow:1. The vermifiltration has effective removal of pollutants from sewage. Theaverage removal efficiencies for CODcr, TP, SS, NH3-N and TN were82.0%,70.6%,94.5%,57.9%and59.0%, respectively, and the final effluent quality meets the tier IIstandards of “Urban Sewage Treatment Plant Pollutant Discharge Standards”(GB18918-2002). The number and average weight of earthworms in filters increasedobviousely, indicating that earthworms have good adaptability, growth andreproduction in vermifiltration.2. Compared with low temperature in winter, the purification of vermifiltration isbetter under high temperature in summer. The temperature of filter bed influences theeffect of water purification, the filter bed temperature and removal rate of CODcr, TP,SS and TN were binomial distribution, while the filter bed temperature and removalrate of NH3-N were exponential distribution. According to the experimental resultsand integrated pollutant removal cases, the suitable temperature range forvermifiltration is12~32℃.3. The removal efficiencies of CODcr, NH3-N and TN were negative linearcorrelative to1.0~4.0m3/(m2·d)condition, while the removal rate of efficiency wasnot mainedly correlative at the same condition. When the hydraulic loading is1.0~2.0m3/(m2·d), the effluent quality meets the tier II standards of “Urban SewageTreatment Plant Pollutant Discharge Standards”(GB18918-2002). However, whenthe hydraulic loading is up to4.0m3/(m2·d), the removal effect of various pollutantsdecreased significantly, and the effluent concentrations of TN cannot meet thenational wastewater discharge requirements.4. The secondary structural design of vermifiltration strengthened anti-hydraulicloading and anti-organic loading of filter. It is crucial to improve the stability ofsewage treatment and quality of final effluent. 5. SOD, CAT and POD activity, GSH and MDA in earthworms showed adownward trend after the first rise. The higher hydraulic loading, the higherenvironmental stress to earthworms. In the hydraulic loading1.0~2.0m3/(m2·d) range,the decreasing of body weight and respiratory rate is small, and earthworms couldadapt to the new environment and play ecological functions better. When hydraulicloading increased to4.0m3/(m2·d), earthworms had stong stress response, long adaptperiod, smaller individual. And they secrete large amounts of function protein, whichleads to tissue protein content increased obviously. The intense environment stesscould even threat to their own survial to escape. It affects the stable operation ofvermifiltration.6. In order to ensure the actual operating results of vermifiltration, achieve stablewater quality standards, and to maintain a good environment for earthworms to makethe vermifiltration play the normal ecology efficacy, it is recommended that theinfluent hydraulic load range is1.0~2.0m3/(m2·d).