Study of Bacterial Activities in Biofilm of Constructed Wetland Wastewater Treatment System

Shama Sehar, . (2015) Study of Bacterial Activities in Biofilm of Constructed Wetland Wastewater Treatment System. Doctoral thesis, Quaid-i-Azam University, Islamabad.

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Abstract

During the last decade, wastewater treatment plants and related research had gained much attention owing to emerging global water crisis and rapidly depleting existing water reservoirs. Among various wastewater treatment technologies, the constructed wetland (CW) technology being a "green technology" is considered as a reliable mean for wastewater treatment due to cost effective, eco-friendly and energy sustainable nature. This dissertation is aimed to study the effects of different macrophytes and presence/absence of eDNA and divalent cation e.g. Ca2+ on biofilm formation in laboratory-scale sub-surface flow hybrid constructed wetland (SS-HCW) for domestic wastewater treatment originated from residential colony and vicinity of Quaid-i-Azam University (QAU) Islamabad, Pakistan. Laboratory scale wetlands, planted with different vegetations were constructed in the format of SS-HCW comprising (vertical flow + horizontal flow + sand filter units) and the performance assessment for these systems on the basis of physico-chemical and microbiological parameters were conducted. The wetland units contained gravel, sand and soil layers as support media while third unit composed of only sand. Efficiencies of these wetlands were tested for three different wetland plants (Brachiaria reptans, Trianthema portulacastrum and Veronica aquatica) and compared with control unit (without vegetation) at different hydraulic retention times (HRTs) of 4, 8, 12, 16, 20, 24 and 28 days. It was observed that not only the presence of vegetation but also type of vegetation affected the majority of tested parameters tested. Among all plants, T. portulacastrum demonstrated superior performance by expressing removal efficiencies more than 70% for all the parameters tested. Further to study in detail microbial association with plants and their biofilm formation, both Gram positive and Gram negative bacteria including Pseudomonas. aeruginosa, Aeromonas. hydrophila, Escherichia. coli, Staphylococcus. aureus, Staphylococcus. epidermidis and Enterococcus. faecalis etc. were isolated from the plants rhizosphere. The role of Ca2+ and extracellular DNA (eDNA) was simultaneously studied in bacterial aggregation and biofilm formation for wastewater treatment. It was found that although Ca2+ had no influence on eDNA release however, the presence of Ca2+ with eDNA favors the bacterial aggregation via attractive acid-base interactions and cationic bridging. Furthermore, isothermal titration calorimetry (iTC) studies strengthen thermodynamically favorable interaction between DNA and Ca2+ by expressing high negative enthalpy (-34.518 KJ/Mole) pointing towards the spontaneous and exothermic nature of the binding process. After establishing role of Ca2+ and eDNA in promotion of biofilm, efficiency of laboratory scale constructed wetland planted with T. portulacastrum was again tested in the presence of Ca2+ (in the form of lime stone). As formally predicted, the Ca2+ addition significantly improved the performance of lab-scale wetland as compared to one operated in the absence of Ca2+. The removal efficiency of BOD5, COD, TSS, TDS, NO3-, NO2-, Cl-, PO43- and SO42- were 94.53, 95.29, 82.72, 89.15, 92.40, 94.88, 87.24, 88.84 and 90.65% respectively whereas the efficiency was 72.34, 80.67, 70.03, 74, 80.14, 81.46, 77.38, 73.69 and 76.59% respectively when run without calcium at same retention time of 20 days. Treatment was also significantly improved in case of removal of microbial contaminants (52.5 CFU/mL and 64.25 MPN index/100 mL with the presence of calcium compared to 5.10 x 103 CFU/mL and 265.5 MPN index/100mL in the absence of calcium). Finally, in-vitro studies were conducted to get more insights into the mechanics of biofilm formation in the absence/presence of calcium. Microscopic analyses (light and electron microscopy) showed a very well organized pattern of biofilm in the presence of calcium as compared to one tested without calcium at different time scales. There was more aggregation of cells on gravels collected from the wetland in the presence of calcium as compared to one without it. Therefore, the present work provides a detailed study on the effectiveness of CWs in wastewater treatment. Besides, the role of vegetation and HRT are very important in improving the treatment efficiency. Also, divalent cations are influential in promoting biofilm formation, which strongly impact on constituent removal efficiency in wastewater. Hence, the same approach can effectively be utilized for pilot scale wetland systems as well as other biofilm mediated wastewater treatment technologies

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: Bacterial, Activities ,Biofilm ,Constructed ,Wetland, Wastewater ,Treatment
Subjects: Q Science > Q Science (General)
Depositing User: Unnamed user with email jmemon@hec.gov.pk
Date Deposited: 26 Oct 2017 04:16
Last Modified: 26 Oct 2017 04:16
URI: http://eprints.hec.gov.pk/id/eprint/6747

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