Study On The Performance Of Vermi-biofilter For Municipal Wastewater Treatment

Over the years,along with the rapid urbanization in China,the sustainable wastewater control technologies have attracted more and more attentions.The research of high-efficient,energy-saving,environment-friendly,decentralized and onsite wastewater systems is one of popular topics.Vermi-biofilter system is this kind of new technology to meet the special requestment of the wastewater treatment in small towns,and have a high potential for application in developing countries. Vermi-biofilter is an ecology system that the earthworm(vermes)is introduced into the conventional biofilter according to modern ecological design conception,which has expanded the original biological chain and enriched the biodiversity of the system.It,should be noted that sewage and sludge synchronous treatment is achieved in the vermin-biofilter system.Accordingly,the performances of the Vermi-biofilter system with the quartz sand and ceramisite grain as the filter medium,respectively,used for the municipal wastewater treatment in small towns were investigated in a pilot plant.The dissertation discussed the processes of municipal wastewater treatment and synchroneously the sludge reduction and stabilization,and described the influence factors on the sewage and sludge treatment.Then,the diversity and functional populations in the vermi-biofilter was analyzed using PCR-SSCP technology.Later, the physiological characteristics adaptation of the earthworm in the vermi-biofilter system,such as the digesting quantity of the organics,the content change of the SOD and CAT was discussed,too.Finally,the cost-effectiveness comparison of the vermi-biofilter with the conventional activated sludge process(CAS)was performed.The principal conclusions were obtained as follows.1.Better organics,SS and NH₄-N removal were achieved using vermi-biofilter for municipal wastewater treatment,when the COD_cr,BOD₅,SS and NH₄-N influent concentrations were in the range of 58.57～78.30 mg/L,29.60～38.40 mg/L,24.31～36.19 mg/L,18.62～24.21 mg/L.respectively,at the organic loadings from 0.46 to 0.93 kgBOD₅·m^-3·d^-1,the wastewater temperature ranged from 7 to 28.6℃.2.The effluent and the removal efficiency of COD,BOD₅,SS and NH₄-N were in the range of 28.94～32.87mg/L,47.26%～57.55%;12.80～15.60mg/L,54.78%～59.29%;7.47～9.10mg/L,62.06%～77.90%;11.29～14.69mg/L,21.01%～52.58%, respectively,in the quartz sand vermi-biofilter system under the experimental conditions.3.The effluent and the removal efficiency of COD,BOD₅,SS and NH₄-N were in the range of 21.17～28.66mg/L,50.64%～64.73%;10.4～15.0mg/L,55.99%～66.36%;7.2～9.77mg/L,57.18%～76.25%;7.64～11.30mg/L,35.53%～67.67%, respectively,in the ceramisite grain vermi-biofilter system under the experimental conditions。4.The removal efficiencies of COD,BOD₅ and NH₄-N by the ceramisite grain vermi-biofilter system were 15.07%,7.39%and 49.70%higher than that by sand quartz vermi-biofilter system.And the removal efficiencies SS was 6.39%lower than that by the quartz sand vermi-biofilter system.No obvious removals on TN and TP were detected.5.The experimental organic loading was in the range of 0.46～0.93 kgBOD₅·m^-3·d^-1which was 4～7 times as that of the conventional biofilter.The reasons can be interpreted in 3 aspects,including the direct digestion on organics by earthworms,higher microorganism quantity due to higher specific surface of the filter medium,the enhancement of the microorganism activity.The quantity of the biofilm in the vermi-biofilter was calculated as 14.67kg/(m³sand quartz),which was 2～4 times as that of conventional biofilter.The specific surfaces of the experimental sand quana and ceramisite grain were 5.25×10⁴ and 9.84×10⁴times as that of conventional biofilter.6.At the organic loading of 0.46～0.93 kgBOD₅·m^-3·d^-1,the influences of the organic loading on the removal of organics,and SS were negative linear correlation. That on the removal of NH₄-N was binomial distribution.No obvious influence was detected on the removal of TN and TP.The experimental results also indicated that the optimal organic loading of the quartz sand vermi-biofilter and the ceramisite grain vermi-biofilter were in the range of 0.78～0.90kgBOD₅/m³Â·d and 0.85～ demonstrated the conclusion.11.The functional microbial in the vermi-biofilter is Bacillaceae,accounting for about 43.3%,most of which is uncultured with strong adaptation.12.The digestion on the sludge organics is a key factor for the sludge reduction and stabilization.The digestion quantity in the experiment in the quartz sand vermi-biofilter and ceramisite grain vermifiltraion were(1.41～5.26)mgOM/(g earthworm)and(2.51～8.48)mg OM/(g earthworm).The results indicated that the earthworms in the ceramisite grain vermifiltraion can utilize more the organics in the sludge for their vital movements,such as synthesis,respiration and reproduction etc.13.With the increase of the hydraulic loadings from 2.4 m³Â·m^-2·d^-1to 6.72 m³Â·m^-2·d^-1,the earthworms can exist well in the vermi-biofilter due to the regulation of the SOD and CAT enzyme to resist the environmental menaces.Compared with the earthworms bred in the cattle excrement,the somatopleure of the earthworms in the vermi-biofilter suffered some damages to some extent.Under the same experimental conditions,the damages in the ceramic grain bed were less than that in the quartz sand bed.14.Compared with CAS process,the vermi-biofilter process is of less investment,less operation cost,simple management.It can be concluded that the total investment was averagely 36%lower and the operation cost was averagely 41.33% less than that of CAS process.Consequently,the vermi-biofilter was more appropriate for the wastewater treatment of the small towns in southern China.