An invariant-region-preserving scheme for a convection-reaction-Cahn–Hilliard multiphase model of biofilm growth in slow sand filters

Development of slow sponge sand filter (SpSF) as a post-treatment of UASB-DHS reactor effluent treating municipal wastewater.

This research work focused on studying water purification without chemical pre-treatment. In the studies, alternative approaches were carried out to develop a filter bed suitable for filtering water without the use of chemical treatments that is also cost effective. Polyvinyl Chloride (PVC) pipes (100 × 1700) mm were used as filter boxes. The experiment carried out during the study was divided into two major parts; that is slow sand and rapid sand filter parameters. The slow sand filter consisted of two filter pipes, one consisting of a stratified layer of sand of size range of 0.20 – 0.60 mm with a depth of 700 mm as filter medium. The turbidity, filtration rate and head loss of the effluent across the filter were monitored for 15 days. It was found that slow sand filter plus granular activated carbon (GAC) and rapid sand filter plus GAC were more effective in the removal of turbidity. Turbidity reduced with the increase in time. Rapid sand filter was found to be the least effective in the removal of bacteria while slow sand filter plus GAC was the most effective. The slow sand filter unit gave a very high coliform count compared to other filter units. It was found that the filtration rate plays a vital role in the mechanism of filtration.

Sand filtration is an important unit operation in the purification of surface water supplies. It is usually achieved by either slow sand or rapid gravity filters. Because slow sand filters require a larger area than rapid filters, a general misconception prevails among decision makers that they are expensive. This is not, however, always true, and for many small water supplies, slow sand filters are appropriate and cost effective.

Investigating spatial and temporal dynamics in microbial community composition of multiple full-scale slow sand filters in drinking water treatment.

Formation and degradation of haloacetic acids (HAAs) in Tai Lake Water Treatment Plant (WTP) in Kin-Men County, Taiwan, were evaluated in this study. The results showed that formation of HAAs after chlorination is a fast process. Owing to the presence of fairly high organic precursors in the raw water, a large amount of HAAs (up to 80 μg/L in summer) was formed after addition of the pre-chlorine, and only a small portion of the HAAs was removed during the coagulation, flotation, and rapid filtration units. However, more than 80% of HAAs were removed in slow sand filtration (SSF) unit. Laboratory batch filtration tests showed that the HAAs can not be effectively removed by conventional coagulation and filtration treatments. However, the HAAs in water was effectively removed by biodegradation in batch biodegradation tests using filter sands taken from the top of the SSF unit in Tai Lake WTP. For comparison with the results obtained in batch experiments, simulated SSF systems were also installed in laboratory to evaluate the effects of biodegradation for HAAs removal in filter columns. Results of parallel laboratory SSF column tests showed that HAAs was quickly degraded when the simulated SSFs have been operated for a suitable time to allow the microbial growth on the sand surface. In both batch and simulated SSF biodegradation treatments, the biodegradation rates for HAAs decreased as the number of halogen atoms increased. The results in this study demonstrated that biological degradation is the major mechanism responsible for HAAs removal in the SSF units.

Slow and rapid sand filtration methods were tested for their ability to remove triactinomyxon actinospores (Tams), the waterborne infective stage of the salmonid parasite Myxobolus cerebralis, from contaminated water. Within the rapid sand filtration treatments, two backflush protocols were tested. The first consisted of extended backflush duration, and the second consisted of diverted flow past the aquaria with fish for 5 min after backflushing. A slow sand filter treatment served as a nonbackflushed control to the two rapid sand filters and also as its own unique filtration technique. Negative and positive controls were run simultaneously and served both slow and rapid sand filters. The sand used consisted only of particles greater than 180 μm (diameter). Triactinomyxon actinospores were regularly introduced to the fish-rearing systems above the sand filters. After 60 d, clinical signs of whirling behavior and black tails were seen among the positive controls. A polymerase chain reaction (PCR) assay for M. cerebralis conducted at the study's conclusion indicated no infection among the negative controls and both of the rapid sand filter treatments. In the slow sand filter treatment 1.6% of all fish were infected, whereas 98% of the positive controls were infected. Portions of the same tissue samples used for the PCR analysis were also assayed according to the pepsin–trypsin digest (PTD) test. Within the rapid sand filters, 2.9% of fish within the long back flush treatment were infected, as were 100% of the positive controls. The diverted backflush, slow sand filter, and negative controls were all negative according to the PTD test. These results demonstrate that the backflush technique is important in the proper function of rapid sand filters used to remove Tams and that both rapid and slow sand filtration could be viable options in treating hatchery water supplies that are contaminated with whirling disease.

Monitoring biofilm function in new and matured full-scale slow sand filters using flow cytometric histogram image comparison (CHIC)

Most rural dwellers in Nigeria depend on contaminated water from ponds, streams and wells for drinking water. Every household needs simple water purification device like Slow Sand Filter (SSF) to prevent water-borne diseases. This study was conducted to determine the effect of Granular Activated Carbon (GAC) particle sizes and depths in SSF on the purification of water. Two sets of SSF were fabricated using 6 inches (15.24cm) diameter PVC pipe, fine sand (0.25 mm grain size) with 35 cm depth. GAC for the first set SSFs (particle sizes 10 mm, 14 mm with 15 cm depth) and GAC for the second set of the SSFs has 15 and 25 cm depths with particle size 10 mm. The SSF has 50 litres storage tank from which raw water flows into the filter chamber (15.25 diameter and 110 cm long PVC). The filter was kept moist for 21 days for schmutzdecke to fully develop which is effective in trapping bacteria. Raw water was poured into the SSF, water samples were collected and analyzed using standard methods. The SSF has a capacity of producing 35 litres/h clean water. Percentage reduction of Lead, Manganese, Copper, Iron, Turbidity and Total Coliform Counts of the filtered water compared with the control were 91.35-99.88%, 90.00-98.33%, 42.00-100.00%, 46.67-100.00%, 13.04-99.15% and 16.67-57.69%, respectively. The SSF increased pH and Calcium by 7.14-27.71% and 83.65-98.21%, respectively. SSF with 10 mm and 25 cm depths GAC reduced the pollutants than the other two filters and it is recommended for purifying pond water.

Slow sand filters (SSFs) are commonly used for treating drinking water, effectively removing contaminants such as particles, organic matter, and microorganisms. However, the ecological dynamics of prokaryotic communities within SSFs remain poorly understood. This study investigated the top sand layer, the Schmutzdecke (SCM), along with the influent and effluent water of full-scale SSFs at four drinking water treatment plants (DWTPs) in the Netherlands. These plants use SSFs as the final step in their treatment to produce unchlorinated drinking water. Two DWTPs treat surface water after dune infiltration and do not apply advanced oxidation processes prior the SSF. In contrast, the other two DWTPs treat reservoir-stored surface water and incorporate ozonation or UV and activated carbon filtration as part of their treatment train. All SSFs consistently reduced biomass in the effluent compared to the influent, confirming their role in biomass load reduction. Key biological and chemical parameters showed that pretreatment with dune infiltration produced more biologically stable drinking water compared to reservoir storage. Moreover, while SSFs act as polishing filters when treating dune-infiltrated surface water, they significantly alter the prokaryotic community and biological stability of the water when treating reservoir-stored surface water. Prokaryotic communities in the SCM and water samples showed distinct compositions rather than merely the accumulation of microorganisms in the SCM from the influent water, demonstrating that SSF are active ecosystems different from water. The SCM exhibited a higher relative abundance of the genera SWB02, Gemmata, Pedomicrobium, Nitrospira, and mle1-7, while in the water samples the genus Candidatus Omnitrophus was relatively more abundant. Moreover, each DWTP hosts a unique prokaryotic profiles in both the SCM and water samples. Source water, upstream treatment and/or the biological stability of the influent water are identified as potential causes affecting the prokaryotic communities in SSFs that affect the microbial water quality of the effluent water.

For over 150 years, slow sand filters have been an effective means of treating water for control of microbiological contaminants. Slow sand filters do not need constant operator attention, making them an appropriate technology for water systems that are small or that employ part-time operators. During the 1970s through the 1990s, research and field evaluations of slow sand filtration have demonstrated its efficacy for control of microbiological contaminants that were unknown in the 1800s. In addition, pretreatment processes such as roughing filters and pre-ozonation have been developed or adapted for use with slow sand filters, increasing the range of source waters that can be treated and the number of contaminants that can be removed in slow sand filters. Inclusion of a layer of granular-activated carbon in a slow sand filter bed has improved capability for control of synthetic organic chemicals. This paper reviews design concepts and process capabilities for slow sand filters and discusses recent innovations in slow sand filter design that now enable this technology to be applied more widely than would have been appropriate two decades ago. Key words: slow sand filter, design, operation and maintenance, microbiological contaminants, small systems, pretreatment.

Using new technologies and sustainable methods to obtain safe and clean water is considered one of the most important aims. In this work, almond shells have been used to prepare an activated carbon (AC) filter. Two types of sand filter media were used to simulate slow and rapid sand filters. Samples of raw water from Tigris River were taken, and the following parameters were studied (pH, turbidity, electrical conductivity (EC), total dissolved solids (TDS), sulphate and heavy metals (Iron(Fe), copper(Cu) and zinc(Zn)). Results showed that replacing sand with AC was better in the removal of Fe and Zn, when a slow sand filter was used the removal was 99% for both of them, while the enhancement in the removal seems to be small when the rapid sand filter was used.

Elimination of terpenoid odorous compounds by slow sand and river bank filtration of the Ruhr River, Germany

In an attempt to obtain a conservative estimate of virus removal during slow sand and river bank filtration, a somatic phage was isolated with slow decay and poor adsorption to coarse sand. We continuously fed a phage suspension to a 7-m infiltration path and measured the phage removal. In a second set of experiments, we fed the phage suspension to 1-m long columns run at different pore water velocities. Using the data obtained, a mathematical model was constructed describing removal vs. pore water velocity (PWV), assuming different statistical distributions of the adsorption coefficient λ. The bimodal distribution best fit the results for PWVs higher than 1 m/d. It predicted a removal of approximately 4 log10 after 50 days infiltration at 1 m/d. At PWVs below 1 m/d the model underestimated removal. Sand-bound phages dissociated slowly into the liquid phase, with a detachment constant kdet of 2.6 × 10⁻⁵. This low kdet suggests that river bank filtration plants should be intermittently operated when viral overload is suspected, e.g. during flooding events or at high water-marks in rivers, in order for viruses to become soil-associated during the periods of standstill. Resuming filtration will allow only a very slow virus release from the soil.

Elimination of terpenoid odorous compounds by slow sand and river bank filtration of the Ruhr River, germany

Nutrient and water use efficiency can be improved in soilless cultivation systems by recirculating the leachate. However, untreated leachate contains particulate matter that may clog drip emitters and root pathogens which can pose a threat to the crop health if reintroduced into the system. To address this issue, an ultraviolet (UV) filter was developed to complement the slow sand filter to enhance its treatment efficiency in removing root pathogens. The experiment was conducted during 2019 and 2020 at Punjab Agicultural University, Ludhiana, Punjab to assess the effectiveness of the UV filter in removing pathogens, specifically Dickey zeae and Xanthomonas, from the leachate in a closed soilless cultivation system. Pre and post-treatment measurements were made 40 days after transplanting (DAT) and 80 DAT to evaluate the efficiency of the UV filter. The results revealed that combined UV and slow sand filters substantially treated the raw leachate. At 40 DAT, the pathogen removal efficiency was 94.8%, while it was 92% at 80 DAT. The findings highlight the importance and effectiveness of using the UV filter as an additional treatment step in closed soilless cultivation systems with significant improvement in the overall removal efficiency of root pathogens from the leachate.