Evaluating household reverse osmosis systems for microbial safety: A case study from Chennai, India.

Effectiveness of household reverse-osmosis systems in a Western U.S. region with high arsenic in groundwater

Radionuclides (uranium, thorium, radium, radon gas etc.) are found naturally in air, water, soil and rock. Everyday, we ingest and inhale these radionuclides through the air we breathe and through food and water we take. Out of the internal exposure via ingestion of radionuclides, water contributes the major portion. The natural radioactivity of water is due to the activity transfer from bed rock and soils. In our surveys carried out in the past few years, we have observed high concentrations of uranium and total dissolved solids (TDS) in drinking waters of some southern parts of Punjab State exceeding the safe limits recommended by national and international agencies. The main drinking water source is the underground water procured from different depths. Due to the highly saline taste, disorders in their digestive systems and other ailments, people are installing reverse osmosis (RO) systems in their houses. Some RO systems have been installed on commercial basis. The state government is also in the process of installing community RO systems at the village level. As high values of uranium are also undesired and may pose health hazards due to radioactivity and toxicity of uranium, we have conducted a survey in the field to study the performance of various RO systems for removal of uranium and TDS. Water samples from about forty RO systems from Faridkot, Mansa, Bathinda and Amritsar districts of Punjab State were collected and analyzed. Our results show that some RO systems are able to remove more than 99% of uranium in the underground waters used for drinking purposes. TDS values are also reduced considerably to the desired levels. So RO systems can be used to avoid the risk of unduly health problems posed by high concentrations of uranium and TDS in drinking water.

The reverse osmosis (RO) system is widely applied to produce reclaimed water for high-standard industrial use. Chlorine disinfection is the main biofouling control method in the RO systems for wastewater reclamation. However, researchers reported the adverse effects of chlorine disinfection which aggravated biofouling in laboratory-scale RO systems. In this study, four parallel 4-inch spiral wound RO membranes were used to study the effect of chlorine on biofouling in a pilot-scale RO system. The free chlorine dosages in four experimental groups were 0, 1, 2 and 5 mg/L, respectively. After continuous chlorination and dechlorination, the feed water entered the RO system. It was found that chlorine pretreatment caused a 1.9–36.7% increase in relative feed water pressure of the RO system, suggesting that chlorine aggravated the membrane fouling in the pilot-scale RO system. The microbial community structures of living bacteria in the feed water of the RO system were determined by the PMA (propidium monoazide)-PCR method and showed that the relative abundance of chlorine-resistant bacteria (CRB) was significantly increased after disinfection. Nine major genera which maintained higher relative abundance in experimental groups with high chlorine dosage were considered as possible key species causing membrane fouling, including Pedobacter, Clostridium and Bradyrhizobium.

This thesis presents a comprehensive research report on microbiological aspects of biofouling occurrence in full-scale reverse osmosis (RO) systems. Biofouling is a process in which microorganisms attach to membranes and develop into a thick film that can choke the entire RO system. Management of this problem requires basic understanding of the mechanism of this phenomenon. The basic questions of this PhD research project therefore addressed the origin, succession and spatiotemporal development of biofilms in full-scale RO systems, in particular in relation to operational aspects of RO systems. The multifaceted research strategy involving acquisitions of representative samples and use of many molecular and microscopic analysis techniques in parallel was employed. The investigation showed that biofilms are able to grow on any surface in a full-scale RO plant. This gives local niches for detachment of biomass, either as single cells or cell clumps, and results in a spreading of bacteria to the further stages of the plant. In the RO membrane modules, the enriched bacteria might more easily colonise the surfaces since they will be better adapted to growth in the system than bacteria present in the feed water. Initially, the single cell colonizers (sphingomonads) form a number of flat and abundantly EPS-embedded cell monolayers over the entire membrane surface. The clumps-associated pioneers (mainly Beta- and Gammaproteobacteria) appear to be trapped mainly in the first part of the module, most likely due to a filtering action of the spacer. In time, these bacteria develop in pillar-like structures and slowly spread throughout the whole membrane module on top of the established sphingomonads biofilm. The secondary colonisers (bacteria and eukaryotes) occur in the resulting biofilm formations. Although composition of the biofilm microbial community undergoes a succession in time, the architecture of an established biofilm appears to be rather stable. Conventional treatment of RO membrane modules with chemicals did not lead to cleaning: the sphingomonads cells can be detected under the collapsed but obviously not removed biofilm EPS matrix. After cleaning, the biofouling layer seemed to grow faster (within 6 days) than a fresh biofilm (16 days). To conclude, biofouling is a complex phenomenon with two appearances: a fouling layer on the membrane limiting the water flux and a fouling layer on the spacer limiting the water flow through the spacer channel and resulting in an increased pressure drop. It became clear that cleaning strategies should focus more on the removal of accumulated biomass and not only on the killing of cells. Moreover, the basal Sphingomonas layer requires further research to appropriately control biofouling in RO systems. It might also be possible to design the RO - membrane module in a different manner, leading to a different biofilm morphology which gives less rise to operational problems.

Chapter 4 - Transport Models, Membrane Materials, and Basic Flow Patterns

A new approach for freshwater production and energy recovery from an oil field

Ground water in both the northeastern and southwestern coast areas of Taiwan may contain high concentrations of arsenic. Since no central water supply system is available in some of those areas, point-of-use (POU) water purification devices are considered as an option for providing safe drinking water. In this study, removal of arsenic, using two types of POU purification devices, reverse osmosis (RO) systems and distillers, was investigated. Three commercially available RO systems and two distillers were selected to test their removal efficiency of arsenic from synthetic and real ground water. Experimental results of the three RO systems using synthetic ground water showed that only one system had good removal efficiency for arsenic. In subsequent experiments using real ground water with 0.7 mg l−1 arsenic, only one RO system was able to meet the drinking water standard after producing about 1,000 l of treated water. For the distilling systems, 99% of the arsenic was removed from both synthetic and real ground water. The arsenic concentrations in the finished water of both distillers were all below the standard for drinking water. Although systems with higher arsenic removal efficiency seemed to have better removal of total dissolved solids (TDS), no correlation could be found after analysis.

As global temperatures rise, water scarcity is becoming a critical issue worldwide, impacting countries like South Africa and Brazil and cities in India such as Gurugram, the focus of this study. One significant source of water wastage is Reverse Osmosis (RO) systems, which generate 3-4 liters of wastewater for every liter of purified water. This study surveyed 143 respondents in Gurugram through a 22-question survey to gather demographic, socioeconomic, and water usage data, including RO system practices. The results revealed that 86% of respondents used RO systems, but only 45% were aware of wastewater reuse practices, and 39.8% actively reused their RO wastewater. Additionally, while 25.2% accurately knew the amount of water wasted by their RO system, 51% believed they knew. 14% of respondents would consider reusing RO wastewater if better technology were available. These findings suggest that limited technology and awareness are the primary barriers to RO wastewater reuse in Gurugram, highlighting the need for increased education on RO system inefficiencies.

The abundance of transparent exopolymer particles (TEPs) in seawater has been reported for many years. Recently, however, TEPs have been implicated as one of the leading causes of biofouling in reverse osmosis (RO) systems. A pilot plant study of a seawater ultrafiltration (UF)–RO system was conducted to monitor seasonal variation of TEPs, removal through pretreatment processes, and deposition in the RO system. Operational performance of the UF and RO systems was also monitored to evaluate the effects of TEPs on plant operations. A spectrophotometric assay measured TEPs in the particulate and colloidal size range at different stages of the plant. TEP monitoring of raw water indicated a significant increase of p-TEPs and c-TEPs from late March until early May, after which TEPs subsided to lower levels. The period was also marked by increased chlorophyll a and total organic carbon, indicating algal blooms in the seawater source. TEPs in the raw water were partially removed by microstraining and UF p...

Removal of metals and assimilable organic carbon by activated carbon and reverse osmosis point-of-use water filtration systems

Monitoring of experimental landfill cells with membrane concentrate infiltration: A systematic assessment of leachate quality and treatment performance

Evaluation of economic feasibility of reverse osmosis and membrane distillation hybrid system for desalination

A modified Assimilable Organic Carbon (AOC) procedure was adopted in conjunction with Heterotrophic Plate Count (HPC) method to assess the effect of Single Effect Distillation (SED) and Reverse Osmosis (RO) lab-scale systems on the biological stability of industrial water. Industrial water was collected from a local Industrial Water Works, pre-treated with alum coagulation and cartridge filtration, before being subjected to advanced water treatment. The results obtained in this study indicated that AOCs in the SED product water were in the range of 70-80 micrograms acetate-C/L, while those in the RO product water ranged from 30-40 micrograms acetate-C/L in the 15-min permeate to 55-65 micrograms acetate-C/L in the 3-hr permeate. The above findings suggested that product water of both systems were potentially biologically unstable and would likely lead to bacteria regrowth during its distribution and storage. Removal efficiencies of lab-scale RO and SED systems on AOC were as high as 90%, dependent on the concentration of AOC-NOX in the industrial water. The RO system had much higher organic removal efficiencies in terms of AOC and DOC than the SED system. Organics removed from both feed waters were found to be concentrated in the brine water and rejected water in SED and RO systems respectively.

On the feasibility of community-scale photovoltaic-powered reverse osmosis desalination systems for remote locations

Chapter 7 - Designing of a Reverse Osmosis System