WATER QUALITY MONITORING AND IDENTIFICATION OF BACTERIAL COMMUNITIES IN BIOFILMS OF NUST WATER STORAGE TANKS

Abstract

Water is one of the crucial driving forces for sound functioning of ecosystem though, this fundamental resource is being polluted at an alarming rate. To showcase the drinking water predicament, current study was conducted to assess the quality of water in terms of its physico-chemical and microbial parameters in water storage tanks of NUST and to identify bacterial communities in biofilms formed within the tanks. Study had two phases in which first phase includes the physico chemical and microbial analysis of water from selected storage tanks for a period of six months including two seasons (pre-monsoon and monsoon). Various physico-chemical parameters were tested which includes pH, dissolved oxygen (DO), electrical conductivity (EC), residual chlorine (Cl), turbidity, hardness, alkalinity, total dissolved solids (TDS), Total suspended solids (TSS), Nitrate and Nitrite to examine the quality of drinking water in two seasons. Overall physico-chemical parameters were found to be within permissible limit set by World Health Organization or Pakistan Drinking Water Quality Standards (WHO/PDWQS) except dissolved oxygen (DO), total suspended solids (TSS) and residual chlorine (Cl) in both seasons. Moreover, bacteriological properties of water samples were also analyzed through most probable number technique (MPN). All water samples were reported to be contaminated microbiologically due to low detection of residual chlorine. Pearson Product Moment correlation matrix depicted a strong correlation among various physicochemical parameters having P value less than or equal to 0.05. Moreover, Paired t test reveals that there is no statistically significant difference between water quality of underground and overhead water storage tanks in both seasons. The second phase of the study aimed to understand the growth of biofilms on two different tank materials including polyvinyl chloride (PVC) and reinforced cement concrete (RCC) and comparison of biofilms growth on these coupons after 15 and 30 days. Bacterial growth was observed more on RCC coupons compared to PVC in most of the samples. Moreover, more bacterial growth was observed after 30 days compared to 15 days in most of the samples, but few samples showed more growth of biofilms after 15 days due to bacterial detachment. The detachment of biofilms is considered a main problem in deteriorating the quality of drinking water in storage tanks. However, bacterial diversity varied and increased with the passage of time. SEM images showed that the structure of biofilm became complex and difficult to comprehend with the passing days. Pb was observed in all the biofilm samples exceeding the permissible limits set by WHO while Mn and Fe were detected in few samples of biofilms. Elemental composition of biofilms showed that all the samples were loaded with high contents of carbon and oxygen which shows that the organic content in the water was higher which further promotes the bacterial growth in biofilms and bacteria were good oxidizing agents and aerobic in nature. This study provides new ideas for the analysis of microbial ecology in drinking water storage tanks especially the tanks made up of reinforced concrete cement (RCC).