Microbiological and physico-chemical assessment of surface water processed with low-cost and sustainable technology

Abstract

Surface water has been used for drinking purpose from ancient times. However, with increasing population and human activity this water became contaminated with pathogens, disease vectors or unacceptable levels of toxins or suspended solids. In Bangladesh, tube wells came as a solution, but soon it turned out to be a menace as it was contaminated with arsenic in many areas. Cities and towns are supplied with expensive large scale water treatment plants but this is not viable for the majority of the population in Bangladesh who live in isolated villages. A similar situation exists in most of the low resource countries of the world. Therefore, small domestic scale solutions for drinking water are needed for villages which are low-cost, simple technology and easy to maintain. Surface water is free of arsenic since it comes mostly from rain and melted snow. As this water seeps through different layers of the ground it picks up different minerals to become ground water aquifers; poisonous arsenic will also be present in the intermediate rocks. Since arsenic is difficult to remove in a domestic scale arrangement while destroying enteropathogenic microorganisms is simpler. So, use of arsenic free surface water treated using different simple techniques could be more desirable for the rural areas of the low resource countries like Bangladesh. From the perspective of human consumption, surface water is contaminated with enteropathogenic microorganisms, including those of diarrhea, cholera, typhoid, paratyphoid, jaundice etc., which need to be removed to make the water safe for drinking. So, the present study was basically taken up with the aim to study and evaluate the success of three new technologies that can disinfect surface water from diarrhoeal disease causing microorganisms. First one is low-cost solar pasteurization device developed by a group of scientists at the Department of Biomedical Physics & Technology (BMPT), University of Dhaka, that can be heated up water to much more than 60 0 C needed to destroy enteropathogenic microorganisms. This solar pasteurizer designed at BMPT automatically allows UV to act on the treated water. So, UV of the sun contributes in destroying diarrhoeagenic microorganisms. Water samples from seven different ponds, lakes and rivers of Bangladesh were subjected to treatment using this device and the highest temperature achieved was 84°C after 4 hours of exposure to sunshine. Regardless of sampling sites, highest reduction of aerobic bacterial population was 4.1±0.7 log CFU/ml recorded in non-selective medium. In another study, a simple and inexpensive water purification method was sought using natural coagulant (moringa seed powder) and antibacterial agents (scallop powder) followed by natural bio-sand filtration. Surface water collected from different sources (e.g. pond, lake and river) were treated with combined moringa seed powder (0.04%) and scallop powder (0.01%) (MOSP) for 30 minutes showed a clear water layer at the top and a sediment layer at the bottom. The clear water was then passed through natural bio-sand filter and the resulting water was found drinkable. Regardless of sampling sites, highest bacterial population reduction of 5.8±0.9 log CFU/ml was recorded in non-selective medium. The microbiological and physico-chemical parameters of the water treated with above two technologies showed non-significant differences compared to the United States Environmental Protection Agency (USEPA) drinking water quality parameters. Spiked study and molecular techniques using Polymerase Chain Reaction (PCR) of uidA gene of E. coli also confirmed the effectiveness of these developed technologies. The shelf-life study of the treated water demonstrated that it can be stored at room temperature up to 6 months without compromising the quality, indicating the usefulness of these two technologies in drinking water scarcity areas of the world, because the ingredients used are readily available, inexpensive, user friendly and natural. On the other hand, the sediment or sludge produced in the second technique could be used in agriculture field after proper application of compost. In this study, third technique was using of metals like brass and its constituents, copper and zinc. The results were obtained depending on the mode of the experiment. With brass filings (granules) in a small amount of water such that the water remains entirely within the brass filings, the bacterial count was found undetectable after about 30 minutes of treatment. On having three plates of these three metals at the bottom of three individual plastic containers containing the water under test and shaken continuously for 30 minutes each, if the water volume was small, having a few mm depth above the plates, brass could reduce the bacterial count to non-detectable values. The counts reduced to some extent by copper followed by zinc but were still detectable. When water volume was large with about 50 mm depth above the metal plates, the count reduced for copper to a large extent, but not much for zinc and brass. However, when the treated samples were stored at room temperature, all resident bacteria along with coliform including E. coli increased to almost original values after 4 hours. This result indicates that the resident microorganisms were possibly injured due to the effect of copper which resuscitated on storage. Thus, the use of copper, brass or zinc plates were not able to destroy bacterial population with practical volumes of water and therefore, this study was not extended further. The present work has shown that the solar pasteurization and the technique of using moringa and scallop powder followed by bio-sand filtration are indeed successful in providing safe drinking water in rural areas of the world and despite many similar water purification systems available commercially, these two new techniques would be the simplest, inexpensive and environmental friendly. These simple and easy treatment and filtration methods are particularly helpful for flood prone areas of Bangladesh, where there is a scarcity of drinking water during flood. The people can easily get safe drinking water if training on these techniques are provided to the village people so that they themselves can make the devices when needed, thus empowering themselves.