EVALUATION OF THE PERFORMANCE OF ANAEROBIC BAFFLED REACTOR FOR DOMESTIC WASTEWATER TREATMENT

Abstract

Many countries in the world are facing some major water related hitches. Some of these are environmental contamination due to over production and mismanagement of wastewater, lack of freshwater availability and water scarcity as well as challenge of pathogens and organic matter removal to meet stringent regulations of drinking water utilities. Among number of technologies used for wastewater treatment, biological treatment (anaerobic digestion) may be an appropriate option for cost-effective and sustainable solution to clean wastewater. Anaerobic digestion is an attractive technology to mitigate a sustainable treatment of organic waste and wastewater being easy management, operation and applicable. The need is to optimize the process of anaerobic digestion by analyzing the operational parameters and microbial consortia prevailing under different conditions within the reactor to make the process economic and sustainable. Anaerobic baffled reactor (ABR) is a multiple chambered single digester/reactor which has many advantages for wastewater treatment. The aim of the present study was evaluation of four chambered anaerobic baffled reactors, one constructed at the treatment site of Quaid-i-Azam University in terms of its efficiency for organic load removal and microbial composition with variation in different environmental conditions and two laboratory scale ABRs. Reduction in organic material present in domestic wastewater (in terms of chemical oxygen demand (COD), total nitrogen, ammonia and sulphates) evaluated at different temperature conditions. For field scale ABR, the overall efficiency gradually increased with increase in temperature preferably at temperature range 28˚C to 34˚C. Maximum COD reduction noticed was 47% at temperature 34˚C. Similarly, maximum sulphates removal was 44 % achieved at 34˚C and total nitrogen removal was 31% at 28˚C. Efficiency of ABR was significantly higher in summer season as compared to winter season. Laboratory scale reactors were also designed similar to field scale and run at two temperatures in incubator, low temperature referred to 5˚-16˚C and high temperature as 41-45˚C. Results of lab scale ABRs indicated that organic matter and pathogens removal was more prominent and consistent at higher temperature as compared to lower temperature ABR. At high temperature ABR, in last three weeks maximum pathogens removal was observed in the effluent, it reduced from 1100 (in influent) to 150/100ml xiii (in effluent). While in low temperature ABR, pathogens reduction was not seen in the start period, reduction was observed in middle period from 1100 to 210/100 ml. To investigate bacterial and archaeal communities, DNA-sequencing with marker gene 16S approach was used coupled with environmental condition (temperature) and chambers of ABR. Analysis of evolution in microbial community profile of samples was done in each alternate month throughout the year for large scale ABR shows variation of microbial community structure along the chambers. Composition of microbial consortia was dissimilar in chamber 1 to 4. Each chamber harbor specific microbial flora of the respective stage as hydrolytic microorganisms in 1st chamber, acidogens in 2nd chamber, acetogens in 3rd chamber and methanogens in 4th chamber. Helicobcteraceae was common family present in ABR and its member Lithotrophicum was leading specie. The second largest group Bacteroidetes were involved in fermentation system and break down of larger components of protein, starch etc. while the 3rd largest phylum Firmicutes mostly prevailed in anaerobic environment and are reported as to produce extracellular enzymes as lipases and proteases for breakdown of organic matter. The striking aspect about the results was rapid apparent change in microbial community composition and dominance along the chambers of ABR within month and between the months. Similarly, significant difference in microbial composition with temperature variation, along the months, during summer and winter season was observed. Microbial evolution was seen along the months, as community structure during start months was completely different than in last months. Proteobacteria was observed as the most prevailing phylum however dominance of phyla was changed with temperature change. Results showed that temperature had more prominent effects on microbial community shift as compared to chamber wise community shift. Significant difference in microbial community structure was observed with temperature change as compared to difference along chamber. Maximum OTUs (195279) were found in sample of April and chamber 1and 3, while minimum OTUs (20138) were found in the month of October chamber and chamber 2. Alpha rarefaction curves showed complete species saturation and richness in all the samples except two samples for the month of October chamber 1 and chamber 2. Significant difference was observed in composition of microbial community with variation in temperature, while community organization along the chamber was less variable. It was observed that some taxa were consistently leading in more than one sample. xiv A wide diversity of bacterial families was detected along 1st and 4th chamber of the reactor. Bacterial community organization was changed along 1st chamber showing that bacterial community composition changed over the time from February to December and new families appeared in 1st chamber of each month. Core bacterial families Helicobacteraceae (absent in December), Commamonadaceae and Desulfomicrobiaceae were shared in almost all months. It is concluded that analysis of microbiota of ABR in the current investigation will enhance the mechanistic understanding of the diversity and biogeography of anaerobic digestion bacterial communities within a theoretical ecology framework and have important implications for microbial ecology and wastewater treatment processes. It will support the process of optimization for future development of more effective wastewater treatment and better effluent quality.