Evaluation of Pilot Scale Trickling Filter System for the Treatment of Wastewater

Abstract

Attached growth wastewater treatment systems are considered to be effective in developing countries due to their low energy, operational and maintenance cost. A trickling filter system is a type of sewage treatment facility which is used to minimize the levels of carbonaceous compounds in tenns of BODs and COD from wastewater in addition to pathogens and NH4-N level. The present research study was mainly focused on to treat domestic wastewater by pilot scale trickling filter systems. For this tenacity. two different types of pilot scale trickli ng filter (TF) systems i.e. one was installed in work station (under shade) located at the vicinity of the Department ofMicrobio)ogy. QAU, Islamabad, Pakistan (setup-I) and the other onc was installed in open environment at residential area ofQAU. Islamabad, Pakistan (setupII), were evaluated with varied temperature conditions, hydraulic load rates (HLR). organic load rates (OLR) and continuous recirculation of effluent over the top of filter bed. In the 151 phase, efficiency of setup-l system was assessed for potential water reuse, and development of a zero order kinetic model defining the efficiency of carbonaceous and microbial pollutant removal under various prevailing temperature conditions. Operational data (both influent and effluent) of 330 days were collected from pilot scale TF system for various parameters. In rainy monsoon, autumn, spring and summer seasons, average percentage reduction were observed in the range of 52-72, 5 I -73, 18-69 and 74-89 % for BODs, COD, TDS and TSS respectively. However in winter season, a high percentage rcduction was observed only for TSS (74-81 %) while for other parameters like BODs, COD and TDS, it was found in the range of 13-50, 12-49 and 23-6 1% respectively. It was also observed that pilot scale treatment facility showed high efficiency in the removal of fecal colifonns i.e. 43-55 and 57-86% average percentage reduction were observed after 151 and 6th day of treatment respectively in all seasons of the year, indicating potential for reuse in irrigation. Moreover, 13 different bacterial species (E. coli, Sabno'lella, Pseudomonas, Enterobacter, Klebsiella, Shigella. Proteus, Alcaligenes, Staphylococcus, Streptococcus. Micrococcus. Coryl1ebacterium and Bacillus spp.) were isolated from the microbial slime layer developed on the surface of stone media. The mathematical model developed based on data can be used to design and optimize low-cost TF systems aimed at water quality improvement for potential wastewater reuse in developing countries. In the 2nd phase, a cost-effective and simple stone media pilot-scale trickling biofilter (TBF) was designed, constructed and operated in a continuous recirculation mode for wastewater treatment with a hydraulic flow rate of 1.2 Umin (Q = 0.072 m3fhr) and hydraulic loading (QlA) ofO. 147 m'/day for 15 weeks at a temperature range of 14.5-36°C. A substantial reduction in the average concentrations of different pollution indicators, such as COD (85.6%), BOD, (85.6%), TDS (62.8%), TSS (99.9%), EC (J 5. 1%), PO, (63.22%), 804 (28.5%) and TN (34.4%), was observed during 15 weeks of operational period. Whereas a considerable average increase in the levels of DO (63.2%) was found after treatment of wastewater by the TBF system. No significant reduction in most probable number (MPN) index of fecal colifonns was observed in the effluent in first 9 weeks of operation. However, a significant reduction in the MPN of fecal colifonns was observed, i.c. 80-90% in the last few weeks of treatment. In the 3rt! phase, stone media setup-ll TBF system was operated under different hydraulic retention time (HRT) i.c. 24, 48 and 72 hrs at a constant flow rate of 0.04 m3/day and it was perceived that stone media pilot scale TBF system showed high efficacy regarding removal of physicochemical and microbiological parameters under different HRTs. It was observed that by increasing HRT up to 48 and 72 hrs, the proficiency of setup- II TBF system increased significantly to reduce different parameters i.e. COD (70.9%), TDS (34%), EC (23.5%), SO. (37%), PO, (81.8%) and TN (66.6%). Furthennore, it was suggested that greater retention time and sand filtration playa key role in the pathogens removal and improvement of water quality. In the 4th phase, a new strategy was evaluated by using integrated media containing pebbles and gravels instead of stone to provide support for the growth of microbial slime layer. Furthennore, the integrated media TBF system was operated at three different flow rates (Q) i.e. 0.004 m' /day, 0.0072 m' /day and 0.01 m' /day and on each particular flow rate, effluent was operated under three different HRTs i.e. 48, 72 and 96 hrs in order to detcnnine the efficiency of integrated media pilot scale TBF system treating domestic wastewater. It was observed that inte&1fated bed material with air space had optimjstic effect over TBF operation and the lowest and intennediate flow rates (0.004 m3/day and 0.0072 ml/day) showed promising results with respect to percent reduction of different physicochemical parameters i.c. COD (74.2-80.5%), TDS (60.3-69.5%), Ee (62.8 -68.6%) and P04 (45.3-60.3%), A significant reduction in TN (59-63.3%) was observed at flow rates of 0.004 ml/day and 0.0072 m3/day. Moreover, it was observed that the efficiency of integrated media pilot scale TBF system in tenns of pathogen removal (CFU/mL) increased signi fi cantly with continuous recirculation of wastewater for an extended period of time under different flow rates. From comparative assessment of stone media and integrated media pilot scale setup-ll TBF system, it was evaluated that integrated media TBF system showed significant activity in the percent reduction of different physicochemical parameters as compared to stone media TBF system. Thus, overall results suggest that pilot-scale TBF has a great potential to be transferred to decentralized treatment system for handling sewage of small communities in developing countries, in order to produce effluent of good quality, which can be safely used for irrigation as well as ornamental purposes.