Biodegradation of the cyanobacterial toxin microcystin LR in natural water and biologically active slow sand filters

A bacterium (MJ-PV) previously demonstrated to degrade the cyanobacterial toxin microcystin LR, was investigated for bioremediation applications in natural water microcosms and biologically active slow sand filters. Enhanced degradation of microcystin LR was observed with inoculated (1 x 10(6) cell/mL) treatments of river water dosed with microcystin LR (>80% degradation within 2 days) compared to uninoculated controls. Inoculation of MJ-PV at lower concentrations (1 x 10(2)-1 x 10(5) cells/mL) also demonstrated enhanced microcystin LR degradation over control treatments. Polymerase chain reactions (PCR) specifically targeting amplification of 16S rDNA of MJ-PV and the gene responsible for initial degradation of microcystin LR (mlrA) were successfully applied to monitor the presence of the bacterium in experimental trials. No amplified products indicative of an endemic MJ-PV population were observed in uninoculated treatments indicating other bacterial strains were active in degradation of microcystin LR. Pilot scale biologically active slow sand filters demonstrated degradation of microcystin LR irrespective of MJ-PV bacterial inoculation. PCR analysis detected the MJ-PV population at all locations within the sand filters where microcystin degradation was measured. Despite not observing enhanced degradation of microcystin LR in inoculated columns compared to uninoculated column, these studies demonstrate the effectiveness of a low-technology water treatment system like biologically active slow sand filters for removal of microcystins from reticulated water supplies.     

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.     

Modeling antimicrobial contaminant removal in slow sand filtration

Slow sand filters are used in rural regions where source water may be subjected to antimicrobial contaminant loads from waste discharges and diffuse pollution. A numerical model (LETA) was derived to calculate aqueous antimicrobial concentrations through time and depth of a slow sand filter and estimate accumulating contaminant mass in the schmutzdecke. Input parameters include water quality variables easily quantified by water system personnel and published adsorption, partitioning, and degradation coefficients. Simulation results for the tetracycline, quinolone, and macrolide classes of antimicrobials suggested greater than 3-log removal from 1 microg/L influent concentrations within the top 40 cm of the sand column, with schmutzdecke antimicrobial concentrations comparable to other land-applied waste biosolids. A 60-day challenge experiment injecting 1 microg/L tylosin to a pilot slow sand filter showed an average 0.1mg/kg of the antimicrobial remaining in the schmutzdecke layer normally removed during filter maintenance, and this value was the same order of magnitude as the sorbed concentration predicted by the LETA model.     

Removal and fate of Cryptosporidium parvum, Clostridium perfringens and small-sized centric diatoms (Stephanodiscus hantzschii) in slow sand filters

The decimal elimination capacity (DEC) of slow sand filtration (SSF) for Cryptosporidium parvum was assessed to enable quantitative microbial risk analysis of a drinking water production plant. A mature pilot plant filter of 2.56m(2) was loaded with C. parvum oocysts and two other persistent organisms as potential surrogates; spores of Clostridium perfringens (SCP) and the small-sized (4-7microm) centric diatom (SSCD) Stephanodiscus hantzschii. Highly persistent micro-organisms that are retained in slow sand filters are expected to accumulate and eventually break through the filter bed. To investigate this phenomenon, a dosing period of 100 days was applied with an extended filtrate monitoring period of 150 days using large-volume sampling. Based on the breakthrough curves the DEC of the filter bed for oocysts was high and calculated to be 4.7log. During the extended filtrate monitoring period the spatial distribution of the retained organisms in the filter bed was determined. These data showed little risk of accumulation of oocysts in mature filters most likely due to predation by zooplankton. The DEC for the two surrogates, SCP and SSCD, was 3.6 and 1.8log, respectively. On basis of differences in transport behaviour, but mainly because of the high persistence compared to the persistence of oocysts, it was concluded that both spores of sulphite-reducing clostridia (incl. SCP) and SSCD are unsuited for use as surrogates for oocyst removal by slow sand filters. Further research is necessary to elucidate the role of predation in Cryptosporidium removal and the fate of consumed oocysts.     

The construction of a sand profile sampler: Its use in the study of the Vorticella populations and the general interstitial microfauna of slow sand filters

A simple and inexpensive method is described by which the component groups of the interstitial fauna can be examined undisturbed by direct microscopy. The method has been developed specifically to locate and enumerate the functional interstitial microfauna of slow sand filters used in water purification and it is designed to demonstrate the spatial relations of the constituent populations as they develop in time in a flowing system. The sampler has been successfully applied to monitoring the development of Protozoa and Rotifera in pilot scale and full scale slow sand filters at the London Metropolitan Water Board's Walton and Ashford Common Treatment Works. Results are presented for the incidence of the general microfauna and for the development, vertical distribution and effect of flow rate on the Vorticella populations.     

Removal of fish pathogenic bacteria in biological sand filters

Documentation is required to evaluate the use of infiltration systems as an alternative method for removal of fish pathogenic bacteria in wastewater from fish-farms. This study was performed to investigate the removal of bacterial fish pathogens in biological sand filters. A second aim of the study was to evaluate the bacteria used in the study in order to find a suitable model organism for future experiments. Low-strength wastewater from an inland freshwater salmonid farm was intermittently loaded (70 mm/day in 24 doses) to filter columns containing either fine sand (d(10)=0.25) or coarse sand (d(10)=0.86). After a wastewater loading period of 10 weeks, separate sand columns were seeded with Yersinia ruckeri, Pseudomonas fluorescens, Aeromonas hydrophila and Aeromonas salmonicida subsp. salmonicida, respectively, for a period of 30 days. All the bacteria showed the same removal performance during the experiment, with a significantly lower removal in the beginning of the experiment (day 1-7) compared to mid- and late-phase (day 12-30). In mid- and late-phase the removal stabilized at a high level (>99.9%) for all the bacteria. The hydrophobic cell surface properties of the Aeromonads were higher than Ps. fluorescens and Y. ruckeri. This can possibly explain the significantly higher (P<0.05) removal efficiencies seen for A. hydrophila and A. salmonicida subsp. salmonicida compared to Y. ruckeri and Ps. fluorescens. Results were promising with regard to the use of low-cost infiltration systems as an alternative disinfection method for fish-farm wastewater. Following the criteria for a suitable model organism (removal efficiency, detection in filter effluent and die-off in storage tanks), Y. ruckeri was found to be a feasible model organism for use in future experiments.     

Clogging in intermittently dosed sand filters used for wastewater treatment

Clogging in intermittent sand filter (ISF) systems was analyzed using an unsaturated flow model coupled with a reactive transport model. Based on the results of a model sensitivity analysis, several variables were determined to be important in the clogging phenomena observed in ISFs, including hydraulic loading rate, influent chemical oxygen demand (COD) concentration, filter dosing frequency, and time of operation. Several modes of operation were identified that minimize the growth of bacteria at the filter surface. Following the sensitivity analysis, several case studies where ISF clogging was documented were simulated using the model. The results from the case study model simulations were found to be correlated with the total suspended solids loading rate (TSSLR) at the point of clogging. A model was developed that relates biomass development at the surface of ISFs with the TSSLR that can be sustained without clogging. The engineering significance of the model is presented in terms of operational and design considerations.     

Contaminants removal by bentonite amended slow sand filter

Earlier studies have indicated that variability in size, surface texture and charge greatly influence the contaminant removal process in granular media. Based on surface characteristics of montmorillonite, it is anticipated that small addition of this clay would increase adhesion sites for bacterial growth and extracellular polymer production in the slow sand filter and thereby enhance its contaminant removal ability. Experiments were performed by permeating groundwater contaminated with pathogens (total coliform and E. Coli) and inorganic contaminants through the bentonite amended slow sand filter (BASSF). Surprisingly, the BASSF retained inorganic contaminants besides pathogens. Water-leach tests (pH of water leachate ranged from 2 to 9) with spent BASSF specimen indicated that the inorganic contaminants are irreversibly adsorbed to a large extent. It is considered that the combined effects of enhanced-organic matter mediated adhesion sites and increased hydraulic retention time enables the BASSF specimen to retain inorganic contaminants. It is envisaged that BASSF filters could find use in treating contaminated groundwater for potable needs at household and community level.     

Corrosion control enhancement from a dolomite-amended slow sand filter

The associated decrease of pH in slow sand filters, due to CO2 conversion and biological activity, may produce effluent that is slightly corrosive to downstream distribution pipe material. This pilot study examined the use of a 3-cm crushed dolomite limestone media layer placed within the filter column of a slow sand filter to enhance effluent corrosion control by the introduction of beneficial dolomite dissolution products, without impacting turbidity removal efficiencies. Turbidity removal, calcium concentration, pH, conductivity, total hardness and alkalinity changes were calculated for the filter during a 60-day pilot study, and water chemistry values were used to estimate the changes of the saturation index (SI) throughout the filter run. Total hardness change through the filter was compared to change calculated by a derived equation for hardness using calcium concentrations to determine if the media was dissolving in stoichiometric proportions, and mineral service life in the filter was estimated using an assumption of stoichiometric dissolution at a constant flow rate. Effluent SI was raised an average of 30%, alkalinity was increased by 19%, and effluent pH averaged 7.7. Filter effluent complied with current turbidity regulatory requirements for the provision of potable water, and mineral service life was estimated between 7.5 and 9.5 years.     

Transport and fate of Cryptosporidium parvum oocysts in intermittent sand filters.

The transport potential of Cryptosporidium parvum (C. parvum) through intermittent, unsaturated, sand filters used for water and wastewater treatment was investigated using a duplicated, 2³ factorial design experiment performed in bench-scale, sand columns. Sixteen columns (dia=15 cm, L=60 cm) were dosed eight times daily for up to 61 days with 65,000 C. parvum oocysts per liter at 15°C. The effects of water quality, media grain size, and hydraulic loading rates were examined. Effluent samples were tested for pH, turbidity, and oocyst content. C. parvum effluent concentrations were determined by staining oocysts on polycarbonate filters and enumerating using epifluorescent microscopy. At completion, the columns were dismantled and sand samples were taken at discrete depths within the columns. These samples were washed in a surfactant solution and the oocysts were enumerated using immunomagnetic separation techniques.

The fine-grained sand columns (d₅₀=0.31 mm) effectively removed oocysts under the variety of conditions examined with low concentrations of oocysts infrequently detected in the effluent. Coarse-grained media columns (d₅₀=1.40 mm) yielded larger numbers of oocysts which were commonly observed in the effluent regardless of operating conditions. Factorial design analysis indicated that grain size was the variable which most affected the oocyst effluent concentrations in these intermittent filters. Loading rate had a significant effect when coarse-grained media was used and lesser effect with fine-grained media while the effect of feed composition was inconclusive. No correlations between turbidity, pH, and effluent oocyst concentrations were found. Pore-size calculations indicated that adequate space for oocyst transport existed in the filters. It was therefore concluded that processes other than physical straining mechanisms are mainly responsible for the removal of C. parvum oocysts from aqueous fluids in intermittent sand filters used under the conditions studied in this research.     

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 3mM 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.     

Extracellular enzyme activities during slow sand filtration in a water recharge plant

Activities of the extracellular enzymes beta-glucosidase and phosphatase and bacterial densities were investigated during the filtration process at several sites in a groundwater recharge plant at the Ruhr river (Hengsen recharge plant in Schwerte. Germany). Low numbers of microorganisms and low levels of activity in this type of habitat, compared to most surface waters, caused methodological problems when determining microbial activity. In this study, fluorigenic model substrates, which enable hydrolytic rates as low as 1 nmol (L x h)(-1) to be measured, were used to determine extracellular enzyme activities. Highest activities were determined in surface water (107 nmol (L x h)(-1) for beta-glucosidase and 252 nmol (L x h)(-1) for phosphatase). which decreased during the filtration process in the gravel prefilter and the main sand filter until the end of subsurface flow (1.6 nmol (L x h)(-1) and 6.8 nmol (L x h)(-1), respectively). Similarly, bacterial numbers decreased from 3.4 x 10(6) to 0.29 x 10(6) cells mL(-1). These data showed that microbial activity within the prefilter and the shallow layers of the sand filter had the greatest impact on water quality. In addition to its involvement in the continuous purification of surface water, the microbial community in the sand filter probably acts as a biological buffer against ephemeral increases in the loads of organic matter and nutrients in the recharge plant.     

Transport and fate of Cryptosporidium parvum oocysts in intermittent sand filters

The transport potential of Cryptosporidium parvum (C. parvum) through intermittent, unsaturated, sand filters used for water and wastewater treatment was investigated using a duplicated, 2³ factorial design experiment performed in bench-scale, sand columns. Sixteen columns (dia=15 cm, L=60 cm) were dosed eight times daily for up to 61 days with 65,000 C. parvum oocysts per liter at 15°C. The effects of water quality, media grain size, and hydraulic loading rates were examined. Effluent samples were tested for pH, turbidity, and oocyst content. C. parvum effluent concentrations were determined by staining oocysts on polycarbonate filters and enumerating using epifluorescent microscopy. At completion, the columns were dismantled and sand samples were taken at discrete depths within the columns. These samples were washed in a surfactant solution and the oocysts were enumerated using immunomagnetic separation techniques.The fine-grained sand columns (d₅₀=0.31 mm) effectively removed oocysts under the variety of conditions examined with low concentrations of oocysts infrequently detected in the effluent. Coarse-grained media columns (d₅₀=1.40 mm) yielded larger numbers of oocysts which were commonly observed in the effluent regardless of operating conditions. Factorial design analysis indicated that grain size was the variable which most affected the oocyst effluent concentrations in these intermittent filters. Loading rate had a significant effect when coarse-grained media was used and lesser effect with fine-grained media while the effect of feed composition was inconclusive. No correlations between turbidity, pH, and effluent oocyst concentrations were found. Pore-size calculations indicated that adequate space for oocyst transport existed in the filters. It was therefore concluded that processes other than physical straining mechanisms are mainly responsible for the removal of C. parvum oocysts from aqueous fluids in intermittent sand filters used under the conditions studied in this research.     

Transport of nanoparticles with dispersant through biofilm coated drinking water sand filters

This article characterizes, experimentally and theoretically, the transport and retention of engineered nanoparticles (NP) through sand filters at drinking water treatment plants (DWTPs) under realistic conditions. The transport of four commonly used NPs (ZnO, CeO_2, TiO_2, and Ag, with bare surfaces and coating agents) through filter beds filled with sands from either acid washed and calcined, freshly acquired filter media, and used filter media from active filter media, were investigated. The study was conducted using water obtained upstream of the sand filter at DWTP. The results have shown that capping agents have a determinant importance in the colloidal stability and transport of NPs through the different filter media. The presence of the biofilm in used filter media increased adsorption of NPs but its effects in retaining capped NPs was less significant. The data was used to build a mathematical model based on the advection-dispersion equation. The model was used to simulate the performance of a scale-up sand filter and the effects on filtration cycle of traditional sand filtration system used in DWTPs.     

利用风积沙研制防渗透气功能砂制品

以西北地区大量风积沙为主要原料,研制同时具有防渗和透气功能的砂制品。以砂治砂,在有效节约水资源的同时改善了生态环境。     

Molecular characterization of microbial populations in groundwater sources and sand filters for drinking water production

In full-scale drinking water production from groundwater, subsurface aeration is an effective means of enhancing the often troublesome process of nitrification. Until now the exact mechanism, however, has been unknown. By studying the microbial population we can improve the understanding of this process. Denaturing gradient gel electrophoresis of PCR-amplified 16S rRNA gene fragments of bacteria, archaea and ammonia-oxidizing bacteria was used to characterize the microbial populations in raw groundwater and trickling filters of an active nitrifying surface aerated system and an inactive non-surface aerated system. Only in the active filter were nitrifying microorganisms found above the detection limit of the method. In ammonia oxidation in this groundwater filter both bacteria and archaea played a role, while members belonging to the genus Nitrospira were the only nitrite-oxidizing species found. The subsurface aerated groundwater did not contain any of the nitrifying organisms active in the filter above the detection limit, but did contain Gallionella species that might play a major role in iron oxidation in the filter.     

Organic carbon removal and nitrification of high strength wastewaters using stratified sand filters

The current practice of spray irrigation of dairy parlour wastewaters is laborious and time consuming. Intermittent sand filtration systems may offer an alternative to spray irrigation when designed to remove organic carbon, nitrogen, phosphorus, coliforms and viruses from such wastewaters to allow discharge of the final effluent directly into receiving waters without damage to the environment. In this study two instrumented stratified sand filter columns (0.425 and 0.9 m deep, and both 0.3 m in diameter) were intermittently loaded for 439 days with synthetic dairy parlour washings at a number of hydraulic and organic loading rates. At a biochemical oxygen demand (BOD) loading of 22 g m(-2) d(-1), over 92% of the BOD and suspended solids in the wastewater was removed in the two filters and nitrification was complete. The 0.9 m column had a sustained ability to adsorb the influent phosphorus during the study period; however, the phosphorus adsorption capacity of the 0.425 m column began to decrease after approximately 30 days. Biomass, comprising hydrated extracellular polymers (exopolymers) and living and dead cells, accumulated in the 0.9 m column; it was assessed by sodium bromide tracer studies and by variations in the sand volumetric water contents using time domain reflectometry (TDR). The biomass growth increased the retention time of the wastewater in the filter media, and occurred mainly at the top of the first sand layer. Intermittent stratified sand filters appear to offer an effective and sustainable treatment process for the removal of BOD from high-strength wastewaters, and for the complete nitrification of ammonium.     

Early strength development in cement-treated sand using low-carbon rapid-hardening cements

Soil stabilization through cementation is a commonly-adopted ground improvement technique in which Ordinary Portland Cement (OPC) is widely used as the binding material. This paper explores the applicability of a low–carbon, rapid-hardening calcium sulfoaluminate (CSA) cement for an accelerated and sustainable soil treatment. This study extensively investigates the early strength development in cement-treated sand with two commercially available CSA cements, through the ultrasonic pulse velocity (UPV) test and the unconfined compressive strength test. UPV evolution curves for the first 24?h are obtained, and the effects of different cement contents and types on pulse velocity and compressive strength at early age are studied. The CSA cements used in this study contain ye’elimite as the main cementing phase with different amounts of calcium sulfate. It is shown that the presence of the calcium sulfates, or lack thereof, significantly influences the initial strength and stiffness gained by the CSA-treated sand. CSA with calcium sulfate develops higher strength in the first 12?h than CSA without calcium sulfate, whereas the 1-day strength is higher for CSA with more ye’elimite phase. The 1-day compressive strength of CSA-treated sand is 2–9 times higher than that of OPC-treated sand, depending upon the cement type and content.