Household Slow Sand Filter Research Articles

Rainwater treatment system efficiency: Household slow sand filter combined with UVC lamp disinfection

A household system to treat rainwater composed of a Household Slow Sand Filter (HSSF) and a commercial ultraviolet lamp reactor was evaluated. Rainwater was collected in the southeast of Brazil (São Carlos, São Paulo) and inoculated with Escherichia coli to simulate contamination. The system was evaluated for 100 consecutive days under real-scale conditions, aiming to remove microbiological and physical-chemical parameters. Results indicated that HSSF removed 1.10 ± 0.33 log of E. coli even with the schmutzdecke in slow formation due to the low concentration of organic matter concentration and scarcity and low diversity of microorganisms in the rainwater. On the other hand, the UV disinfection (UV dose of 30 mJ/cm2) presented an average removal of 4.60 ± 0.58 log, with 87.5 % of the samples presenting absence of microbiological risk. No significant improvement in physical-chemical water quality after the household treatment was observed due to the high quality of raw rainwater. Therefore, it was recognised that rainwater quality was not substantially improved by the HSSF (i.e., filtration could be dispensed) and only UVC lamp disinfection would be enough to produce drinking water. Recontamination was observed during the tests, as weather events and monitored parameters were capable of highlighting the importance of safe storage practices.

Household slow sand filters in intermittent and continuous flow for a long-term surface water treatment: Efficiencies assessment and operational challenges

The Household Slow Sand Filter (HSSF) is a Point-Of-Use technology that has several technical, constructive, and operational advantages, which allows users to improve the quality of their own drinking water at home. This paper aims to provide results concerning the real possibility of treating surface water using HSSF with two feeding strategies, covering more than one year of operation (430 days), including seasons with different inputs on surface water. To do this, we compared the intermittent (HSSF-I) and the continuous (HSSF-C) feeding strategies in quantitative terms (filtered water quality and treatment efficiency) and qualitative terms (construction, cost, and operational challenges). Overall, both HSSF models were efficient and improved the water quality, but HSSF-C produced better quality filtered water in terms of turbidity (73 ( ± 20)% versus 69 ( ± 18)%), Escherichia coli (2.06 ( ± 0.60) log versus 1.65 ( ± 0.78) log), Giardia cysts (>3 log versus 2.89 ( ± 0.32) log), and Cryptosporidium oocysts (1.22 ( ± 0.10) log versus 0.95 ( ± 0.45) log) than HSSF-I. In addition, HSSF-C was able to remain more stable throughout the entire operation, without major impacts caused by influent water variations and maintenance activities. On the other hand, HSSF-I was cheaper, took up less space in the house, had a simple and easy operation, and did not require as much maintenance as the continuous one. Results indicated that HSSF-C may be a more viable model for treating surface water, but it still needs to improve its transfer requirements and assess its user acceptability from field experiences.

Efficiency of a multi-barrier household system for surface water treatment combining a household slow sand filter to a Mesita Azul® ultraviolet disinfection device

Low-cost household technologies for water treatment are crucial to improving drinking water quality and preventing health, social and economic impacts, mostly in middle- and low-income regions. This work assessed the removal efficiency of physical-chemical and bacteriological parameters from river water by a multi-barrier household water treatment system for 113 consecutive days. This system combines a pre-treatment step through a non-woven synthetic blanket, filtration by an intermittent household slow sand filter (HSSF) and a Mesita Azul® ultraviolet disinfection device. In general, the water quality was improved by the evaluated system. Turbidity was removed by an average of 73% (ranging from 33 to 94%), total coliforms (TC) of 3.88 log10 (ranging from 2.22 to 5.16 log10) and E. coli of 2.49 log10 (ranging from 1.81 to 3.30 log10). Filtration improvement was mostly correlated to HSSF biofilm development and influent water quality. Characterisation of HSSF schmutzdecke demonstrated a predominance of organic content, and a higher presence of carbohydrates than proteins on the sand and the blanket. Ultraviolet disinfection with Mesita Azul® inactivated most of the remaining bacteria after filtration and no regrowth was observed after 15 days of disinfection. In conclusion, the multi-barrier household water treatment system was efficient in treating river water, reducing risks of microbial contamination to achieve safe drinking water.

Household slow sand filter efficiency with schmutzdecke evaluation by microsensors

ABSTRACT Slow sand filtration is a common technology providing potable water in rural households across Latin America, Asia and Africa. Two PVC household slow sand filters (HSSF) were operated in continuous (C-HSSF) and intermittent (I-HSSF) flow modes for eight consecutive months. A non-woven blanket was installed on the fine sand top to facilitate cleaning with scheduled maintenance undertaken every 30 days. The efficiency of each HSSF was evaluated via physico-chemical indicators (reduction of turbidity and colour) with biological performance assessed via total coliform and E. coli enumeration post treatment. There were no statistically significant differences between the continuous flow and intermittent flow models for physical–chemical and total coliform reduction parameters. However, when evaluating E. coli, C-HSSF performed better (p = 0.02). The non-woven blanket was subjected to weekly analysis using a Clark-type amperometric microsensor (diameter < 20 µm), which measured dissolved oxygen (DO) concentration in the adherent biofilm. DO microprofiles illustrated a variation in biofilm growth, which were associated with a progressive increase in the HSSF efficiency. The maximum DO depletion value measured during several months of operation showed no significant difference between I-HSSF and C-HSSF (p = 0.98). The microsensor measurements provided unprecedented results in real time. These results can help to understand the efficiency of the filter in relation to the biofilm growth, the dissolved oxygen depletion and turbidity removal.

Filter media depth and its effect on the efficiency of Household Slow Sand Filter in continuous flow

This study evaluated the impact of a 50% reduction of filter media depth in Household Slow Sand Filters (HSSFs) on continuous flow to remove physicochemical and microbiological parameters from river water. Furthermore, simple pre-treatment and disinfection processes were evaluated as additional treatments. Two filter models with different filtration layer depths were evaluated: a traditional one with 50 cm media depth (T-HSSF) and a compact one (C-HSSF) with 25 cm. HSSFs were fed with pre-treated river water (24-h water sedimentation followed by synthetic fabric filtration) for 436 days at a constant filtration rate of 0.90 m3 m−2 day−1 with a daily production of 48 L day−1. Sodium hypochlorite (2.0 mg L−1 of NaOCl 2.5% for 30 min) was used to disinfect the filtered water. Water samples were analysed weekly for parameters such as turbidity, organic matter, colour and E. coli, among others. Removal of protozoan cysts and oocysts by the HSSFs were also evaluated. After pretreatment, turbidity from the HSSF river water was reduced to 13.2 ± 14.6 NTU, allowing the filters to operate. Statistical analysis indicated no significant difference (p > 0.05) between T-HSSF and C-HSSF efficiencies in all evaluated parameters throughout operation time. Hence, media depth reduction did not hinder continuous HSSF performance for almost all the evaluated parameters. However, it may have affected Giardia cysts retaining, which passed through the thinner media on one evaluation day. Disinfection was effective in reducing remaining bacteria from filtered water; however, it was ineffective to inactivate protozoa. The reduction in the filtration layer did not affect the overall filtered water quality or quantity showing that a compact HSSF model may be a viable option for decentralized water treatment.

Household slow sand filters in continuous and intermittent flows and their efficiency in microorganism’s removal from river water

ABSTRACT This study aimed to evaluate the efficiency of four household slow sand filter (HSSF) models for the removal of microorganisms from river water throughout the development of their biological layers (schmutzdecke). Two models were designed to be operated continuously (HSSF-CC and HSSF-CT) and two intermittently (HSSF-ID and HSSF-IF). Filters were fed daily with 48 L pre-treated river water (24 h sedimentation followed by filtration through a non-woven synthetic blanket). Water samples were quantified by coliform group bacteria and analysed by bright field microscopy to visualize the microorganisms. Total coliform reduction was between 1.42 ± 0.59 log and 2.96 ± 0.58 log, with continuous models showing a better performance (p-values < 0.004). Escherichia coli reduction varied from 1.49 ± 0.58 log to 2.09 ± 0.66 log and HSSF-IF, HSSF-CC and HSSF-CT presented a similar performance (p-values > 0.06), slightly better than the one presented by HSSF-ID (p-value=0.04). Microorganisms, such as algae, protozoa and helminths were detected by microscopy in raw water and pre-treated water. Algae were the most significant group in these samples, although they were not visualized by bright field microscopy in the filtered water. Results showed the potential of HSSF in microbiological risk reduction from river water, which increases the range of point-of-use water treatments in rural communities. However, additional studies of the HSSF biological layer must be performed.

Household slow sand filter to treat groundwater with microbiological risks in rural communities

Household slow sand filters (HSSFs) improve the quality of life in rural communities as they provide safe water. However, HSSFs require time for the growth of the biological layer (schmutzdecke) to achieve maximum performance, especially when groundwater is used as it normally has few nutrients. In this ripening period, pathogenic microorganisms can pass through the filter. In this context, this study reports the performance of two HSSF settings, intermittent (I-HSSF) and continuous (C-HSSF) flows followed by disinfection with sodium hypochlorite to treat groundwater with Escherichia coli, Giardia muris cysts and Cryptosporidium parvum oocysts. The weekly introduction of river water was tested as a filter-ripening agent and this procedure reduced the ripening time in approximately 80 days. Filtered water disinfection improved the water quality and inactivated protozoa. The costs and operational challenges addressed in this study can provide support to HSSF technology transfer in rural communities worldwide.

Ripening of household slow sand filter by adding fish food

Abstract Vulnerable communities can improve their quality of life using point-of-use water treatment technologies. Among these technologies, household slow sand filters (HSSF), which are filters adapted to domestic operations, stand out as one of the most effective and sustainable alternatives. However, some technical issues are not fully understood, such as the ripening process, which may take a long time to take place. In this context, this research evaluated the performance of a HSSF, in real scale and operated in continuous flow when a source of nutrients (fish food) was added to influent water, as a potential ripening agent. Physicochemical and microbiological parameters were evaluated to estimate the filter efficiency. According to the results, the HSSF reached a partial ripeness level in a short time with target parameter reduction in filtered water. Nevertheless, the instability observed in the filtered water quality reveals the significant health risks associated with human consumption when the HSSF is not yet ripened.

Household slow sand filters in intermittent and continuous flows to treat water containing low mineral ion concentrations and Bisphenol A

Household slow sand filter (HSSF) has been used as an alternative to drinking water treatment in rural communities worldwide; however, its performance to treat influent water with quality similar to rainwater still needs further studies. Rainwater presents low pH and slight mineral ion concentrations, an aspect that can modify the filter media and consequently the HSSF efficiency. Furthermore, house roofs used in rainwater harvesting can be made of plastic. Therefore, it can introduce chemicals such as Bisphenol A (BPA) in the water. In this context, two pilot-scale HSSFs operated in continuous and intermittent flows were evaluated to treat water containing BPA and low mineral ion concentrations in order to assess the filter performance. Filter media leaching was noticed in the trials; thus, filter media and construction material selection must be carefully evaluated to eliminate risks of pollutant occurrence in drinking water. Operational differences between continuous and intermittent flows influenced the HSSF efficiency for BPA and DOC removals; even so, the filters’ performance was low probably due to the slow schmutzdecke development. According to tracer test results, HSSF can be classified as a plug flow reactor and strategies to improve its hydraulic performance are not required.

Pretreatment using Opuntia cochenillifera followed by household slow sand filters: technological alternatives for supplying isolated communities

ABSTRACT Household slow sand filter (HSSF) performance in continuous and intermittent flows was evaluated when influent water was treated with a natural coagulant extracted from Opuntia cochenillifera. The water under study, used as influent, had a turbidity of 111 ± 17.3 NTU. When clarifying the water with O. cochenillifera, the best condition obtained was 30 mg L−1 in natural pH (without correction), generating clarified water with turbidity satisfactory to filters operation (7.83 ± 2.32 NTU). The results indicated a better performance of continuous flow HSSF in turbidity removal (79.2% ± 8.39%) and higher efficiency of intermittent flow HSSF in the removal of E. coli (2.86 log ± 0.79 log for 12 h pause period and 2.41 log ± 0.42 log for 4 h pause period). For the sake of comparison, the evaluated HSSFs had the same production (60 L day−1). The impact on the interruption of the 96-h feed into the HSSFs was analysed and the results indicated a significant change in the quality of the filtered water after resuming the operation. This fragility of technology must be considered when it is implemented as lack of water can be a reality in the target communities. Acute toxicological assays with C. xanthus larvae showed no toxicity for pretreated and filtered water; however, more testing should be performed.

Microcystis aeruginosa and microcystin-LR removal by household slow sand filters operating in continuous and intermittent flows

A household slow sand filter (HSSF) is a widely used water treatment technology recognized as one of the most effective and sustainable in reducing waterborne diseases. However, there is a lack of knowledge concerning its behaviour in the presence of cyanobacteria and cyanotoxins. In this context, the study aimed to evaluate HSSF ability to remove Microcystis aeruginosa cells (stain BB005) and microcystin-LR from water, among other parameters, when operated under continuous (C-HSSF) and intermittent (I-HSSF) flows. CHSSF was operated at a constant filtration rate (1.22 m3 m-2 day-1), while I-HSSF was operated at a variable filtration rate (starting at 2.95 m3 m-2 day-1 and finishing at zero). Each filter produced 60 L day-1. The influence of the pause period was also tested in the I-HSSF. The water from the study was prepared by inoculating M.aeruginosa culture in water from a well to a final cell density of ± 1 × 105 cells mL-1. M.aeruginosa removal rates were 2.39 ± 0.34 log and 2.01 ± 0.43 log by CHSSF and I-HSSF, respectively. Microcystin-LR concentration in studied water was 5.55 μg L-1, and both filters produced filtered water with microcystin concentrations below 1.0 μg L-1, the maximum value recommended by the World Health Organization (WHO), for most of the samples. Turbidity and apparent colour were also within WHO guidelines. Filters operating with different flow regimes and distinct residence times did not statistically influence treatment efficiencies. Both filters showed promising results in the M.aeruginosa and microcystin-LR removals from water; nevertheless, more research is needed to understand the mechanisms involved in the reduction of both cyanobacteria and cyanotoxin through household slow sand filtration.

Influence of PPCPs on the performance of intermittently operated slow sand filters for household water purification.

Removal of pharmaceuticals and personal care products (PPCPs) from drinking water is usually enhanced by advanced oxidation which is not affordable in low income countries. Slow sand filtration has been found to be capable of removing anti-inflammatory compounds, and its low maintenance costs and easy operation make it an attractive technology for treating drinking water in many parts of the world. In addition, slow sand filters can be used at both large and household scales. The biofilm (i.e. schmutzdecke) developed on the top of the sand and within the upper layers of the sand is acknowledged to be responsible for the water purification. However, it is possible that the PPCPs may affect the schmutzdecke development and microbial community within the filters, and consequently the performance of the filter. This study investigated two household slow sand filters (for water purification) operated intermittently with and without contamination by six PPCPs. Eleven parameters were monitored in the affluent and effluent water, including bacterial species present and schmutzdecke biomass development. Results demonstrated that the household slow sand filter performance was not affected by the 2μgL-1 of PPCPs in the water. There was no significant difference between filters for total coliforms and E. coli removal, but there was considerable difference between sampling times. Biomass considerably increased with the number of filtrations in both filters and there was no significant difference between filter biomass. However, it was found that more bacterial species were present in the period with no contamination than during the contamination period. Bacillus anthracis and Exiguobacterium sp. showed to be resistant to the effects of the PPCPs. These suggest there are effects of PPCPs on bacterial species within the filter. However, the effect of the PPCPs on biomass was not conclusive in this study and needs to be further investigated.

Influence of operating parameters on the performance of a household slow sand filter

The biosand filter (BSF), an intermittently operated household slow sand filter, is one of the commonly used household water purification methods in the rural areas of developing countries. In this study, long-duration tests were conducted in the laboratory to investigate the influence of two important operating parameters, namely the pause period (idle time) and the charge volume on the performance of BSF by using full-scale BSFs. The filters were charged daily with 20 or 40 L of tap water spiked with Escherichia coli or sewage with different pause periods. Results indicated that during the ripening (maturation) of the filter, which took about one month, E. coli removal was low, with an average value &amp;lt;90.0%. Maximum E. coli reduction observed in the test was around 3 log10 units. Doubling the daily charge volume from 20 L to 40 L significantly reduced E. coli removal by at least one log10 unit. Reducing residence time within the filter also impaired the filtrate quality. Cleaning of the filter considerably reduced the bacterial removal efficiency. The aesthetic quality of treated water was good, with a mean effluent turbidity of &amp;lt;1.5 NTU, and was not affected by the variations in charge volume and pause period.

Virus attenuation by microbial mechanisms during the idle time of a household slow sand filter

The biosand filter (BSF) is a household slow sand filter that is operated intermittently such that an idle time of typically 18–22 h occurs in between daily charges of water. Virus attenuation during the idle time was investigated over repeated daily filtration cycles to capture the effect of media aging that encompasses processes occurring throughout the filter depth rather than restricted to the schmutzdecke at the media surface. A threshold aging period of about one to two weeks was required before virus attenuation began. The observed rates of MS2 and PRD-1 reduction were first-order and reached maxima of 0.061- and 0.053-log per hr, respectively, over seven-to-ten weeks. Suppression of microbial activity by sodium azide eliminated virus reduction during the idle time thus indicating that the operative media aging process was microbially mediated. The mechanism of virus reduction was not modification of media surfaces by physical/chemical or microbial processes. Instead, it appears that the activity of the microbial community within the filter is responsible. The most likely biological pathways are production of microbial exoproducts such as proteolytic enzymes or grazing of bacteria and higher microorganisms on virus particles. Implications of these findings for BSF design and operation and their relevance to other biological filtration technologies are discussed.

Performance evaluation of biosand filter modified with iron oxide-coated sand for household treatment of drinking water

The biosand filter (BSF), intermittently operated household slow-sand filter, was modified by introducing a 10-cm thick layer of iron oxide-coated sand. Long-duration (about four months) tests were conducted to compare the performance of the modified BSF (MBSF) with the conventional BSF in terms of their efficiency in removing bacteria and turbidity under different operating conditions. Filters were charged daily with 20L or 40L natural canal water (turbidity 10.0±1.2 NTU; faecal coliforms 365±251 MPN/100mL; pH 8.4±0.4) or seeded tap water (turbidity 14.7±4.3 NTU; Escherichia coli 3850±736CFU/mL; pH 7.9±0.3). Results showed that the performance of MBSF in terms of faecal coliform and E. coli removals was better by at least one-log10 unit throughout the filter operation. The mean bacterial removal was low for BSF for the first month (90.0%), while it was 99.3% for MBSF during the same period. Bacteria and turbidity removals increased with time as filter ripening (maturation) occurred in both the filters. No significant difference was observed in turbidity removal between BSF and MBSF, and mean effluent turbidity was around 1 NTU for BSF and MBSF representing >90% removal. When daily charge was increased from 20L to 40L, a reduction in bacterial removal was noted in both the filters indicating the influence of operating conditions. Effluent physico-chemical quality remained within the guideline values for drinking water.