STUDIES ON FACTORS AFFECTING VERMIFILTRATION FOR WASTEWATER TREATMENT

Abstract

Pollutants removal through ecological system is regarded as the most viable means of decentralized wastewater treatment, as even at present there is a large gap between generation and treatment of wastewater which emphasizes the use of such technologies that could overcome these issues. The treatment systems that require relatively low costs, energy, and maintenance are preferable for the treatment of domestic wastewater. Hence, this work is an attempt to arrive at a consensus on treatment of these pollutants in a single arrangement using vermifiltration process. It comprise mainly of storage tank, wastewater distributer and the treatment unit. The major gaps identified in order to pursue the experimental work were emphasized on optimization of factors affecting vermifiltration process, as it depends on Earthworm’s population (Stocking Density), Hydraulic Loading Rate (HLR) and Hydraulic Retention Time (HRT). In addition to this for evaluating the potential impacts of physical characteristics on the overall performance of vermifilter different kinds of material such as river bed material, wood coal, glass ball and mud ball as a media have been tried. Several laboratory experiments were conducted to evaluate the effect of stocking density (varied from 5000 to 30000 worms/cum of vermifilter bed), filter media and hydraulic loading rate (varied from 0.5 to 2.5 m3m-2d-1) on vermifiltration process. Four types of media were used for experimentation, i.e. (a) River bed material, (b) Wood coal, (c) Glass balls and (d) Mud balls. Besides, the vermifilter was evaluated against varying degree of organic shock loads 675-1410 mg/L of COD. The main conclusions inferred from the study are presented below. In Phase-I effect of earthworm’s stocking density on vermifiltration was evaluated. The stocking density of 10000 worms/cum of vermifilter bed was found to be relatively better as compared with other stocking densities like 5000, 15000, 20000, 25000 and 30000 worms/cum, to achieve the requisite quality of effluent. The results showed that effluent quality of vermifilter with 10,000 W/cum exhibited highest percentage removal of BOD (90%), COD (68%) and total suspended solids (70%). The average reduction of the population of indicator organisms i.e. TC, FC, FS and E. coli was observed as 3.61±0.90, 3.14±0.67, 2.73±0.37 and 2.27±0.28 log unit, respectively to the levels considered acceptable for either recreation or irrigation. The growth pattern of earthworm (E. fetida) Studies on Factors Affecting Vermifiltration for Wastewater Treatment Department of Civil Engineering, IIT Roorkee v showed a maximum individual biomass (121.4%) and growth rate (0.94 g wt. worm−1 day−1) in earthworm’s stocking density of 10000 worms/cum. Phase-II emphasized on identification of suitable media as a vermifilter bed. Vermifilter was evaluated using different material as a media like river bed material, wood coal, glass balls and mud balls. River bed material was found to be relatively better as a media in vermifilter for better growth of earthworm biomass and achieve the requisite quality of effluent. The results demonstrated that effluent quality of vermifilter having river bed material showed highest percentage removal of BOD (78%), COD (71%) and total suspended solids (73%). The average reduction of the population of indicator organisms i.e. TC, FC, FS and E. coli was observed as 3.6±0.90, 3.4±0.67, 2.5±0.51 and 3.32±0.62 log unit, respectively. In reactor VFR maximum earthworm biomass was observed with 73% increment. Phase-III is concerned with the effect of hydraulic loading rates on the performance of vermifilter. When the comparison was carried out among different HLRs like 0.5, 1.0, 1.5, 2 and 2.5 m3m-2d-1 the optimum hydraulic loading rate was observed to be vary in the range of 1-1.5 m3m-2d-1. Vermifiltration system represented perfect efficacy when it was compared with conventional geofilter with better quality of effluent. It observed to be having higher hydraulic conductivity as compared to geofilter. At HLR of 1.0 m3m-2d-1 the removal of various pollutant i.e. BOD, COD and TSS was observed as 86.9, 79.6 and 68.9%, respectively. While at HLR of 1.5 m3m-2d-1 it was resulted as 85.5, 73.9 and 76.1%, respectively. During study, the augmented earthworm biomass increased significantly with increase in HLR up to 1.0 m3m-2 d-1, above which the biomass growth gets reduced. Comparative study on hydraulic aspects of vermifilter and geofilter at different hydraulic loading rates indicated that hydraulic conductivity decreased from its initial value of 0.005 cm/sec as taken when the vermicompost was placed in both the reactors. However, it was more than that a conventional geofilter due to channelization in vermifilter through earthworms. Phase-IV confined with development and design of vermifilter on the basis of outcomes from Phase I, II and III, for effective treatment of domestic wastewater. During this phase a comparison was also carried out between vermifilter and geofilter. The results demontrated that in vermifilter removed a considerable amount of BOD, COD, TSS and indicator organisms as compared to the conventional geofilter. In vermifilter the average COD removal efficiency was observed as 76% while in geofilter it was found as 63%. Similarly, about 85% average BOD removal efficiency was exhibited in vermifilter while in geofilter it Studies on Factors Affecting Vermifiltration for Wastewater Treatment Department of Civil Engineering, IIT Roorkee vi was observed to be 71%. The results of three month study revealed that the presence of earthworms in vermifilter could efficiently remove TC, FC, FS and E. coli and the effluent concentration were observed as 2.89×102 ± 1.14×102, 1.38×102 ± 1.11×102, 1.86×101 ± 0.56×101 and 9.26×101 ± 0.85×101, respectively. While in geofilter it was observed as 5.30×103 ± 0.91×103, 4.30×103 ± 2.32×103, 7.31×102 ± 1.76×102 and 1.90×103 ± 9.48×102, respectively. This implies that vermifilter is able to bring indicator organisms to levels considered safe for irrigation as compared to conventional geofilter. When organic shock loads on vermifilter was applied by increasing the influent COD concentration from 1.5 to 3 times of normal values, the system recovered quickly. It proves its resilience power against organic shock loads, as no significant changes was noted on the performance during vermifiltration process. Results obtained in this study indicated that vermifilter employing Eisenia Fetida help to guarantee the organics removal efficiency and stability of vermifilter if subjected to organic shock loads. This study also promotes an understanding of organic matter removal in the system and experimental results can be used for estimating treatment efficiency of full-scale reactors under similar operational conditions. Kinetic study revealed that the biological degradation of organics follows first-order kinetics with respect to initial sCOD concentration during vermifiltration process. The treated effluent and final vermicompost both were found to be rich in nitrate and phosphate which can be used for agriculture purpose.