Performance Of Slow Sand Filters Research Articles

System dynamic modelling to assess the influential factors affecting roughing filter and slow sand filter performance in treating culinary wastewater

This research aimed to determine the factors that influence the performance of a slow sand filter (SSF) equipped with a roughing filter (RF) as a pretreatment unit using system dynamic (SD) modelling. STELLA was used to model the system and predict the behavior pattern, as well as the system's performance in removing turbidity, total suspended solids (TSS), BOD, COD, and phosphate. SD modelling consisted of system identification, system model framework, model structure building, system modelling, verification, and validation. Two sub-models were obtained from the main model, consisting of the RF and SSF sub-models. Results showed that dissolved oxygen (DO) and the growth rate of microorganisms played significant roles in the parameter removal. Predicted result by SD modelling showed a good fit with actual run, suggesting that factors applied in the model building were adequate to exhibit the actual system. RF removed 80.5 %–85 % of turbidity and 70.63 %–85 % of TSS, while SSF removed 48.50 %–82.43 % of turbidity, 0.92 %–46.15 % of TSS, 1.65 %–65.45 % of BOD, 22.69 %–65.22 % of COD, and 7.96 %–27.11 % of phosphate. Effluent after SSF was still having BOD and COD concentrations exceeding the governmental standard, in which increasing DO inlet and microorganism growth rate were simulated afterward. The scenarios used showed a positive impact on the removal of BOD and COD, resulting in an average concentration lower than the permissible limit (5 mg/L and 50 mg/L, respectively).

Performance of slow sand filters in the after-treatment of effluent from Pernambuco state textile center

Jean laundering generates significant effluent flows with a high organic load, color, and other pollutants, making it difficult to adjust effluent releases within legal limits. Slow Sand Filters (SSF) with downflow were tested for seven days (bench scale), to propose an after-treatment of effluents from an Effluent Treatment Plant of a jean laundry. The research evaluated the removal of the following parameters: color, turbidity, chemical and biochemical oxygen demand, conductivity, ammonia, total phosphorus and salinity of the textile effluent. The experimental apparatus had four SSF: the first filter was fed with distilled water, while the other three filters (triplicates) were fed with effluent. The filters had, on average, the following removal efficiencies: 91% for ammonia, 61.24% color, 89.43% turbidity, and 83.54% for phosphorus. Regarding the removal of organic matter, 98.11% for BOD and 81.17% for COD, demonstrating that SSFs were efficient in removing particulate, dissolved materials and organic matter.

Performance of geotextile-based slow sand filter media in removing total coli for drinking water treatment using system dynamics modelling

In a slow sand filter, a biological layer consisting of alluvial mud and various types of microorganisms grows and attaches to the sand media and forms a matrix called schmutzdecke. Changes to several factors, including the quality of raw water, filtration speed, and the addition of media, affect the performance of the slow sand filter unit in producing treated water. Geotextiles can be equipped to improve the performance of a slow sand filter in removing pollutants. The selection of several factors that affect slow sand filter performance can be used as a starting point for the engineering system to determine the best pattern of performance behavior. This approach was carried out by looking at the dynamic behavior patterns of slow sand filter system performance in treating raw water. This research has not yet been conducted extensively. The dynamic behavior pattern approach to the performance of the slow sand filter unit was used to obtain the behavior model for the schmutzdecke layer on the filter. The system dynamic approach focused on treatment scenarios that can determine the behavior of the slow sand filter system. Several factors were assessed, including temperature, turbidity, nutrient concentration, algal concentration, bacteria and dissolved oxygen. Model simulation results show that the comparison of C: N: P values affected the performance of the schmutzdecke layer in removing total coli. The slow sand filter unit was capable of producing treated water with a total amount of coli equal to 0 on the C: N: P values of 85: 5.59: 1.25, respectively, and a 9 cm geotextile thickness.

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.

Bioaugmentation Mitigates the Impact of Estrogen on Coliform-Grazing Protozoa in Slow Sand Filters.

Exposure to endocrine-disrupting chemicals (EDCs), such as estrogens, is a growing issue for human and animal health as they have been shown to cause reproductive and developmental abnormalities in wildlife and plants and have been linked to male infertility disorders in humans. Intensive farming and weather events, such as storms, flash flooding, and landslides, contribute estrogen to waterways used to supply drinking water. This paper explores the impact of estrogen exposure on the performance of slow sand filters (SSFs) used for water treatment. The feasibility and efficacy of SSF bioaugmentation with estrogen-degrading bacteria was also investigated, to determine whether removal of natural estrogens (estrone, estradiol, and estriol) and overall SSF performance for drinking water treatment could be improved. Strains for SSF augmentation were isolated from full-scale, municipal SSFs so as to optimize survival in the laboratory-scale SSFs used. Concentrations of the natural estrogens, determined by gas chromatography coupled with mass spectrometry (GC-MS), revealed augmented SSFs reduced the overall estrogenic potency of the supplied water by 25% on average and removed significantly more estrone and estradiol than nonaugmented filters. A negative correlation was found between coliform removal and estrogen concentration in nonaugmented filters. This was due to the toxic inhibition of protozoa, indicating that high estrogen concentrations can have functional implications for SSFs (such as impairing coliform removal). Consequently, we suggest that high estrogen concentrations could impact significantly on water quality production and, in particular, on pathogen removal in biological water filters.

Effect of shading on performance of slow sand filters

This research investigated the effect of shading on three slow sand filters, each 1.65 m in diameter. One filter (designated “sun”) served as the control and was open to the sun and sky, the second filter (designated “shaded”) was partly shaded to exclude direct sunlight, and the third (designated “covered”) was completely shaded. All three filters were operated at filtration rates of 0.1 and 0.2 m/h using the same influent raw water. Research was conducted in the summer season when algal activity is at its peak. The performance of the filters was assessed on the basis of filtrate quality and length of filter run. Statistical evaluation of the physicochemical quality of filtrate was performed. Quantitative estimation was made of phytoplankton and zooplankton in the raw and filtered waters. Results indicated that in a tropical country, shading of slow sand filters may help reduce the algal activity in the filters without materially affecting the filter performance.

The role of aluminum in slow sand filtration

Engineering enhancement of slow sand filtration has been an enigma in large part because the mechanisms responsible for particle removal have not been well characterized. The presumed role of biological processes in the filter ripening process nearly precluded the possibility of enhancing filter performance since interventions to enhance biological activity would have required decreasing the quality of the influent water. In previous work, we documented that an acid soluble polymer controls filter performance. The new understanding that particle removal is controlled in large part by physical chemical mechanisms has expanded the possibilities of engineering slow sand filter performance. Herein, we explore the role of naturally occurring aluminum as a ripening agent for slow sand filters and the possibility of using a low dose of alum to improve filter performance or to ripen slow sand filters.

Performance evaluation of slow sand filters using fuzzy rule-based modelling

The main objective of this study is to evaluate and predict the performance of slow sand filters used for wastewater treatment. The uncertainties in the control parameters and processes require fuzzy sets to be used when modelling system performance. Fuzzy logic if– then rules were used to build a model for the removal efficiency (total coliforms) of slow sand filters. The data were collected from three pilot-scale slow sand filters at the Alkhobar (Saudi Arabia) wastewater treatment plant. The removal efficiency of filters was modelled using three input control parameters—filtration rate, sand bed depth and grain size. Based on available data, fuzzy logic if– then rules were established. The fuzzy rule-based model was validated using experimental data of three case studies reported in the literature. The results were also compared with a multiple regression model. A possibilistic risk analysis was performed using optimal removal efficiency of the slow sand filters. The risk is estimated with respect to non-compliance of unrestricted agricultural reuse standards (100 total coliform/100 ml). In addition to slow sand filters, post- or pre-chlorination of wastewater is recommended to improve wastewater quality for conforming agricultural reuse standards.

Enhancing slow sand filter performance with an acid-soluble seston extract

An acid-soluble extract was obtained from Cayuga Lake (Ithaca, NY) seston and applied to slow sand filters at different application rates. Biological activity in the filters was inhibited with 3 mM sodium azide. The filters were challenged with a synthetic raw water containing Escherichia coli. The Cayuga Lake seston extract (CLSE) fed filters removed up to 99.9999% of the influent coliforms while the control filter (no CLSE) removed 50%. Filter performance was correlated with the amount of CLSE applied to the filters.

Computer-aided simulation of slow sand filter performance

Although the modelling of deep bed filtration has progressed considerably in recent years, almost no attention has been given to simulating the process of slow sand filtration. The exception, to date, is the work of Woodward and Ta (1988) who have attempted to simulate slow sand filter performance via a simple, empirical headloss model; however, this model is not deterministic in nature and cannot predict filtrate quality nor the spatial headloss development with the filter. This paper describes the development and calibration of a computer-based numerical model based on assumed filtration coefficient and headloss relationships. The model structure includes a simple representation of biomass development but ignores the possible influence (currently uncertain) of a Schmutzdecke-surface skin. It is concluded that the spatial and temporal headloss development within the media bed can be simulated if certain combinations of headloss and filtration coefficient relationships are assumed.

Evaluating the Performance of Slow Sand Filters in Northern Idaho

Three slow sand filter plants in northern Idaho were studied to evaluate their ability to produce good quality water and to control Giardia cysts, to determine the effects of design and operating factors on treatment performance, and to assess the effectiveness of monitoring and sanitary surveys. During the one‐year study, the plants were sampled weekly for measurement of turbidity, total and fecal coliforms, and heterotrophic plate count. Samples were also analyzed for Giardia cysts and particulates. Results showed that if a slow sand filter is designed and operated according to accepted standards, it should provide consistent and effective water treatment, including a reduction in the concentration of Giardia cysts.

Performance of slow sand filters in refugee water supplies in Somalia

Performance of slow sand filters in refugee water supplies in Somalia