Removal Of Fecal Indicator Bacteria Research Articles

Treatment of Dairy Farm Runoff in Vegetated Bioretention Systems Amended with Biochar

Nitrogen and fecal indicator bacteria (FIB) in runoff from concentrated animal feeding operations (CAFOs) can impair surface and groundwater quality. Bioretention systems are low impact nature-based technologies that can effectively treat CAFO runoff if modified with an internal water storage zone (IWSZ) or amended with biochar. In this study, the performances of four pilot-scale modified bioretention systems were compared to assess the impacts of (1) amending bioretention media with biochar and (2) planting the systems with Muhlenbergia. The system with both plants and biochar amendment had the best performance, with an average of 5.58 log reduction in E. coli and 98% removal of total nitrogen (TN). All systems treated the first pore volume well as new runoff flushed the treated water from the IWSZ. Biochar improved TN and FIB removal due to its high capacity to adsorb or retain ammonium (NH4+), dissolved organic nitrogen, dissolved organic carbon, and E. coli. Planting improved performance, possibly by increasing rhizosphere microbial activity.

Effectiveness of two wastewater disinfection strategies for the removal of fecal indicator bacteria, bacteriophage, and enteric viral pathogens concentrated using dead-end hollow fiber ultrafiltration (D-HFUF)

Primary influent and final effluent samples were collected from wastewater treatment plants using either chlorination or ultraviolet (UV) disinfection biweekly for one year. Paired measurements were determined for fecal indicator bacteria (Escherichia coli and enterococci), cultivated bacteriophages (somatic, F+, and CB-390 coliphage and GB-124 Bacteroides phage), human-associated viral markers (human polyomavirus [HPyV] and crAssphage), enteric pathogens (adenovirus, noroviruses genogroups I and II) as well as total infectious enteric virus. To increase the probability of detecting low concentration targets, both primary (10L) and final effluent wastewater samples (40-100 L) were concentrated using a dead-end hollow-fiber ultrafilter (D-HFUF). Despite seasonal temperature fluctuations, concentration shifts of FIB, bacteriophages, human-associated viruses, and viral pathogens measured in primary influent samples were minimal, while levels of infectious enteric virus were significantly higher in the spring and fall (P range: 0.0003–0.0409). FIB levels measured in primary influents were 1–2 log10 higher than bacteriophage, human-associated viral markers (except crAssphage) and viral pathogens measured. FIB displayed the greatest sensitivity to chlorine disinfection, while crAssphage, adenoviruses and infectious enteric viruses were significantly less sensitive (P ≤ 0.0096). During UV treatment, bacteriophages F+ and GB-124 were the most resistant of the culturable viruses measured (P ≤ 0.001), while crAssphage were the most resistant (P ≤ 0.0124) overall. When UV lamps were inactive, infectious enteric viruses were significantly more resilient to upstream treatment processes than all other targets measured (P ≤ 0.0257). Similar to infectious enteric viruses and adenoviruses; GB-124, F+, and crAssphages displayed the highest resistance to UV irradiation, signaling a potential applicability as pathogen surrogates in these systems. The use of D-HFUF enhanced the ability to estimate removal of viruses through wastewater treatment, with the expectation that future applications of this method will be used to better elucidate viral behavior within these systems.

Removal of Fecal Indicator Bacteria by River Networks

Fecal contamination is a significant source of water quality impairment globally. Aquatic ecosystems can provide an important ecosystem service of fecal contamination removal. Understanding the processes that regulate the removal of fecal contamination among river networks across flow conditions is critical. We applied a river network model, the Framework for Aquatic Modeling in the Earth System (FrAMES-Ecoli), to quantify removal of fecal indicator bacteria by river networks across flow conditions during summers in a series of New England watersheds of different characteristics. FrAMES-Ecoli simulates sources, transport, and riverine removal of Escherichia coli (E. coli). Aquatic E. coli removal was simulated in both the water column and the hyporheic zone, and is a function of hydraulic conditions, flow exchange rates with the hyporheic zone, and die-off in each compartment. We found that, at the river network scale during summers, removal by river networks can be high (19–99%) with variability controlled by hydrologic conditions, watershed size, and distribution of sources in the watershed. Hydrology controls much of the variability, with 68–99% of network scale inputs removed under base flow conditions and 19–85% removed during storm events. Removal by the water column alone could not explain the observed pattern in E. coli, suggesting that processes such as hyporheic removal must be considered. These results suggest that river network removal of fecal indicator bacteria should be taken into consideration in managing fecal contamination at critical downstream receiving waters.

Microbiological evaluation of constructed wetlands and solar disinfection in wastewater treatment and reuse.

The objective of this study was to evaluate the removal of fecal indicator bacteria and select bacterial pathogens (total coliforms, Escherichia coli, Shigella spp., Salmonella spp. and Pseudomonas aeruginosa) in vertical flow constructed wetlands (VF-CWs) with earthworms and solar disinfection (SODIS) as post-treatment of effluent from a septic tank. There was no significant difference between them in removing bacteria using a VF-CW with earthworms (VF-CW W/E) and without earthworms (VF-CW N/E). Both VF-CWs did not completely remove pathogens; however, with the SODIS technology receiving the effluent from VF-CW W/E, for E. coli, Shigella spp., Salmonella spp. and P. aeruginosa, the values were reduced below the limit of detection and 4.3 log unit average reduction for total coliforms, with 6 h in SODIS.

Manure Consistency and Weathering Affect the Removal of Fecal Indicator Bacteria from Grass-Covered Soil

Animal manures contain bacteria which may be used to indicate the potential microbial pollution of irrigation and recreation water sources. The objective of this work was to research how the release of these indicators to runoff is affected by the concurrent influence of the manure consistency and the duration of manure weathering between rainfall events. Liquid and solid dairy manure was applied on grassed soil boxes. The percentage of manure-borne bacteria removed in runoff over 1 hour was determined after the initial rainfall immediately after manure application and after rainfalls that occurred 1 week and 2 weeks after the initial rainfall. The runoff delay was linearly related to the time between rainfalls and was significantly affected by both weathering duration and manure consistency (P = 0.017 and 0.038, respectively). The runoff delay was dependent on the antecedent gravimetric soil water content (R2 = 0.92 and 0.99 for liquid and solid manure treatments, respectively). Manure weathering caused a substantial decrease in the removal of fecal bacteria with runoff in the 2-week weathering compared with the 1-week weathering treatments for both of E. coli and enterococci (P = 0.063 and 0.049, respectively). Every day of weathering decreased the percentage of the released E. coli and enterococci by about 1.2 and 1.5 times, respectively, for both manure consistencies. Manure consistency was not found to significantly affect the percentages of E. coli or enterococci removed with runoff for any level of weathering. Results indicate the need of correcting existing manure bacteria removal models by accounting for manure consistency and weathering duration.

Removal of fecal indicator bacteria and antibiotic resistant genes in constructed wetlands.

Wastewater discharge evidently increased bacterial diversity in the receiving waterbodies. The objective of this study was to evaluate the effectiveness of a constructed wetland in reducing fecal indicator bacteria (FIB) and antibiotic resistant genes (ARGs). We determined the prevalence and attenuation of fecal indicator bacteria including Escherichia coli and enterococci, along with ARGs, and human-associated Bacteroidales (HF183) markers by quantitative polymerase chain reaction (qPCR) method. Three types of water samples (inlet, intermediate, and outlet) from a constructed wetland were collected once a month from May to December in 2013. The overall reduction of E. coli was 50.0% based on culture method. According to the qPCR result, the overall removal rate of E. coli was only 6.7%. Enterococci were found in 62.5% of the wetland samples. HF183 genetic marker was detected in all final effluent samples with concentration ranging from 1.8 to 4.22 log10 gene copies (GC)/100ml. Of the ARGs tested, erythromycin resistance genes (ermF) were detected in 79.2% of the wetland samples. The class 1 integrase (intI1) was detected in all water samples with concentration ranging from 0.83 to 5.54 log10 GC/100ml. The overall removal rates of enterococci, HF183, intI1, and ermF were 84.0%, 66.6%, 67.2%, and 13.1%, respectively.

Multiple Pathways to Bacterial Load Reduction by Stormwater Best Management Practices: Trade-Offs in Performance, Volume, and Treated Area.

Stormwater best management practices (BMPs) are implemented to reduce microbial pollution in runoff, but their removal efficiencies differ. Enhanced BMPs, such as those with media amendments, can increase removal of fecal indicator bacteria (FIB) in runoff from 0.25-log10 to above 3-log10; however, their implications for watershed-scale management are poorly understood. In this work, a computational model was developed to simulate watershed-scale bacteria loading and BMP performance using the Ballona Creek Watershed (Los Angeles County, CA) as a case study. Over 1400 scenarios with varying BMP performance, percent watershed area treated, BMP treatment volume, and infiltrative capabilities were simulated. Incremental improvement of BMP performance by 0.25-log10, while keeping other scenario variables constant, reduces annual bacterial load at the outlet by a range of 0-29%. In addition, various simulated scenarios provide the same FIB load reduction; for example, 75% load reduction is achieved by diverting runoff from either 95% of the watershed area to 25 000 infiltrating BMPs with 0.5-log10 removal or 75% of the watershed area to 75 000 infiltrating BMPs with 1.5-log10 removal. Lastly, simulated infiltrating BMPs provide greater FIB reduction than noninfiltrating BMPs at the watershed scale. Results provide new insight on the trade-offs between BMP treatment volume, performance, and distribution.

Predictive Power of Clean Bed Filtration Theory for Fecal Indicator Bacteria Removal in Stormwater Biofilters

Green infrastructure (also referred to as low impact development, or LID) has the potential to transform urban stormwater runoff from an environmental threat to a valuable water resource. In this paper we focus on the removal of fecal indicator bacteria (FIB, a pollutant responsible for runoff-associated inland and coastal beach closures) in stormwater biofilters (a common type of green infrastructure). Drawing on a combination of previously published and new laboratory studies of FIB removal in biofilters, we find that 66% of the variance in FIB removal rates can be explained by clean bed filtration theory (CBFT, 31%), antecedent dry period (14%), study effect (8%), biofilter age (7%), and the presence or absence of shrubs (6%). Our analysis suggests that, with the exception of shrubs, plants affect FIB removal indirectly by changing the infiltration rate, not directly by changing the FIB removal mechanisms or altering filtration rates in ways not already accounted for by CBFT. The analysis presented here represents a significant step forward in our understanding of how physicochemical theories (such as CBFT) can be melded with hydrology, engineering design, and ecology to improve the water quality benefits of green infrastructure.

Disinfection and removal of human pathogenic bacteria in arctic waste stabilization ponds.

Wastewater stabilization ponds (WSPs) are commonly used to treat municipal wastewater in Arctic Canada. The biological treatment in the WSPs is strongly influenced by climatic conditions. Currently, there is limited information about the removal of fecal and pathogenic bacteria during the short cool summer treatment season. With relevance to public health, the objectives of this paper were to determine if treatment in arctic WSPs resulted in the disinfection (i.e., removal of fecal indicator bacteria, Escherichia coli) and removal of selected human bacterial pathogens from the treated effluent. The treatment performance, with focus on microbial removal, was assessed for the one-cell WSP in Pond Inlet (Nunavut [NU]) and two-cell WSP in Clyde River (NU) over three consecutive (2012-2014) summer treatment seasons (late June-early September). The WSPs provided a primary disinfection treatment of the wastewater with a 2-3Log removal of generic indicator E. coli. The bacterial pathogens Salmonella spp., pathogenic E. coli, and Listeria monocytogenes, but not Campylobacter spp. and Helicobacter pylori, were detected in the untreated and treated wastewater, indicating that human pathogens were not reliably removed. Seasonal and annual variations in temperature significantly (p<0.05) affected the disinfection efficiency. Improved disinfection and pathogen removal was observed for the two-cell system in Clyde River as compared to the one-cell system in Pond Inlet. A quantitative microbial risk assessment should be performed to determine if the release of low levels of human pathogens into the arctic environment poses a human health risk.

Effects of submerged zone, media aging, and antecedent dry period on the performance of biochar-amended biofilters in removing fecal indicators and nutrients from natural stormwater

Biochar has demonstrated promising performance as an amendment to biofilter soil media in removing fecal indicator bacteria (FIB) from simulated stormwater. However, there is no study that investigates its efficacy in treating natural stormwater runoff. Additional information, including the effects of antecedent dry period, microbial biofilm, and presence of a saturation zone on the performance of biochar-augmented biofilters are needed to inform their field implementation. This study uses laboratory column experiments to monitor FIB (enterococci and Escherichia coli) and nutrient removal capacity of biochar-amended biofilters for 140days using natural stormwater. Our study also investigates the effects of antecedent dry days (ADD) and the presence of a saturation zone (SZ) on the performance of lab-scale biochar-amended biofilters. The results suggest insignificant influence of the ADD and SZ on FIB removal performance, however biofilters with a SZ perform significantly better in removing nitrate-nitrogen compared to those without a SZ. In addition, it appears that the presence of biofilm augments nutrient removal capacity but reduces FIB removal capacity. Our observations indicate that biochar-amended biofilters are able to treat (to comply with recreational water quality standard for FIB) urban stormwater runoff for the duration of the experiment. Nitrate- and ammonium-nitrogen removal in the biologically aged biofilters is found to be 50–60% while the total dissolved phosphorus and the organic nitrogen removal is 20–30%. Our results inform full-scale design of biochar-amended biofilters in order to meet the total maximum daily load (TMDL) and municipal separate storm sewer system (MS4) permitting requirement for FIB and nutrients.

Monitoring and predicting the fecal indicator bacteria concentrations from agricultural, mixed land use and urban stormwater runoff

While the urban runoff are increasingly being studied as a source of fecal indicator bacteria (FIB), less is known about the occurrence of FIB in watershed with mixed land use and ongoing land use and land cover (LULC) change. In this study, Escherichia coli (EC) and fecal streptococcus (FS) were monitored from 2012 to 2013 in agricultural, mixed and urban LULC and analyzed according to the most probable number (MPN). Pearson correlation was used to determine the relationship between FIB and environmental parameters (physicochemical and hydrometeorological). Multiple linear regressions (MLR) were used to identify the significant parameters that affect the FIB concentrations and to predict the response of FIB in LULC change. Overall, the FIB concentrations were higher in urban LULC (EC=3.33–7.39; FS=3.30–7.36log10MPN/100mL) possibly because of runoff from commercial market and 100% impervious cover (IC). Also, during early-summer season; this reflects a greater persistence and growth rate of FIB in a warmer environment. During intra-event, however, the FIB concentrations varied according to site condition. Anthropogenic activities and IC influenced the correlation between the FIB concentrations and environmental parameters. Stormwater temperature (TEMP), turbidity, and TSS positively correlated with the FIB concentrations (p>0.01), since IC increased, implying an accumulation of bacterial sources in urban activities. TEMP, BOD5, turbidity, TSS, and antecedent dry days (ADD) were the most significant explanatory variables for FIB as determined in MLR, possibly because they promoted the FIB growth and survival. The model confirmed the FIB concentrations: EC (R2=0.71–0.85; NSE=0.72–0.86) and FS (R2=0.65–0.83; NSE=0.66–0.84) are predicted to increase due to urbanization. Therefore, these findings will help in stormwater monitoring strategies, designing the best management practice for FIB removal and as input data for stormwater models.

Rainfall intensity effects on removal of fecal indicator bacteria from solid dairy manure applied over grass-covered soil

The rainfall-induced release of pathogens and microbial indicators from land-applied manure and their subsequent removal with runoff and infiltration precedes the impairment of surface and groundwater resources. It has been assumed that rainfall intensity and changes in intensity during rainfall do not affect microbial removal when expressed as a function of rainfall depth. The objective of this work was to test this assumption by measuring the removal of Escherichia coli, enterococci, total coliforms, and chloride ion from dairy manure applied in soil boxes containing fescue, under 3, 6, and 9cmh−1 of rainfall. Runoff and leachate were collected at increasing time intervals during rainfall, and post-rainfall soil samples were taken at 0, 2, 5, and 10cm depths. Three kinetic-based models were fitted to the data on manure-constituent removal with runoff. Rainfall intensity appeared to have positive effects on rainwater partitioning to runoff, and removal with this effluent type occurred in two stages. While rainfall intensity generally did not impact the parameters of runoff-removal models, it had significant, inverse effects on the numbers of bacteria remaining in soil after rainfall. As rainfall intensity and soil profile depth increased, the numbers of indicator bacteria tended to decrease. The cumulative removal of E. coli from manure exceeded that of enterococci, especially in the form of removal with infiltration. This work may be used to improve the parameterization of models for bacteria removal with runoff and to advance estimations of depths of bacteria removal with infiltration, both of which are critical to risk assessment of microbial fate and transport in the environment.

Meeting the criteria: linking biofilter design to fecal indicator bacteria removal

The capture, treatment, and reuse of storm‐water runoff are win–win propositions that can lead to improvements in both human water security and ecosystem health. Although not all treatment technologies facilitate the capture, treatment, and reuse of water, biofilters do. Biofilters are engineered analogues of natural systems that use low energy, natural processes to treat stormwater. Biofilter design is closely linked to treatment efficiency. As such, specific design components, such as submerged zones (SZs: saturated, organic‐rich layers near the base of biofilters), can significantly affect contaminant removal. Of particular interest, is the utility of SZ biofilter designs for removing indicators of pathogens, the so‐called fecal indicator bacteria (FIB). FIB exist at high concentrations in stormwater, sometimes several orders of magnitude above recreational, nonpotable reuse, or drinking water standards, and have been identified as one of the primary barriers to stormwater reuse. A comparison of FIB removal values from literature indicates that SZ systems significantly enhance FIB removal (∼10‐fold) relative to other design configurations (p &lt; 0.05). Processes that may contribute to this effect include physicochemical filtration, biofilm formation, and protistan grazing, amongst others. A high degree of synergy exists between processes, and many unknowns remain. Model frameworks developed for evaluation of similarly synergistic systems, including biofilter analogues like the vadose zone, may be useful for addressing these unknowns and informing future biofilter design. WIREs Water 2015, 2:577–592. doi: 10.1002/wat2.1096This article is categorized under: Engineering Water &gt; Sustainable Engineering of Water Engineering Water &gt; Water, Health, and Sanitation

Efficacy of biochar to remove Escherichia coli from stormwater under steady and intermittent flow

Biofilters, designed to facilitate the infiltration of stormwater into soil, are generally ineffective in removing bacteria from stormwater, thereby causing pollution of groundwater and receiving surface waters. The bacterial removal capacity of biofilters has been shown to be lower in the presence of natural organic matter (NOM) and during intermittent infiltration of stormwater. To improve the removal of fecal indicator bacteria (Escherichia coli) under these conditions, we amended sand with 5% (by weight) biochar, a carbonaceous geomedia produced by pyrolysis of biomass, and investigated the removal and remobilization of E. coli. Three types of biochar were used to evaluate the role of biochar properties on the removal. Compared to sand, biochar not only retained up to 3 orders of magnitude more E. coli, but also prevented their mobilization during successive intermittent flows. In the presence of NOM, the removal capacity of biochar was lower, but remained higher than sand alone. The improved retention with the biochar amendment is attributed to an increase in the attachment of E. coli at the primary minimum and to an increase in the water-holding capacity of biochar-amended sand, which renders driving forces such as moving air–water interfaces less effective in detaching bacteria from grain surfaces. Biochars with lower volatile matter and polarity appear to be more effective in removing bacteria from stormwater. Overall, our results suggest that a biochar amendment to biofilter media has the potential to effectively remove bacteria from stormwater.

Persistence of fecal indicator bacteria in sediment of an oligotrophic river: Comparing large and lab-scale flume systems

In this study, both a lab and a large-scale flume system were used to investigate the survival of fecal indicator bacteria (FIB) in bed sediments of an alpine oligotrophic river. To determine the influence of substratum on persistence, survival within 3-cm-deep substratum cages versus on thin, biofilm-covered ceramic tiles was tested. Moreover, the impact of bed shear stress on survival in bed sediments was explored.It was seen that in the lab-scale flume having a very low bed shear stress (0.3 N m−2), E. coli and enterococci survival in 3-cm-deep substratum cages was nearly the same as in a thin biofilm (200 μm). However, in the large-scale flume system characterized by a bed shear stress of 9 N m−2, the added protection of the deeper substratum cages promoted considerably longer survival of E. coli and enterococci than the thin biofilm. Additionally, the FIB removal mechanisms in the two flume systems varied. At the lab-scale, enterococci was seen to persist twice as long as E. coli, while in the large-scale flume the two FIB were removed at the same rate. A comparison of qPCR analyses performed in both flumes suggests that bed sediment erosion and the influence of grazers/predators were responsible for FIB removal from the sediments in the large-scale flume, whereas in the lab flume FIB inactivation caused removal. These results indicate that hydraulic parameters such as bed shear stress as well as the presence of macroinvertebrates in a system are both important factors to consider when designing flumes as they can significantly impact FIB persistence in sediments of fast-flowing, alpine streams.

Variation of raw wastewater microbiological quality in dry and wet weather conditions

The microbiological quality of urban wastewaters presents important environmental, sanitary, and political challenges. However, the variability of untreated wastewater quality is seldom known when it comes to microbial parameters. This study aims to evaluate the variability of microbiological quality in wastewater influents from different wastewater treatment plants connected to combined and partially separate sewer networks in the Parisian area and to evaluate the impact of this variability on the treatment efficiency and on the accuracy of wastewater effluent monitoring. The densities of fecal indicator bacteria (FIB), Escherichia coli and intestinal enterococci, and their partitioning on settleable particles were analyzed at the inlet of two wastewater treatment plants during dry weather (130 composite samples and 7days sampled every 2hours) and storm events (39 composite samples, and 7 rain courses) from 2008 to 2012. The results showed that fecal indicator densities vary according to the network characteristics and according to the meteorological conditions. During storm events, a significant dilution of E. coli and enterococci was observed, as well as a decrease in the settleable fraction of E. coli during the maximal impact of the storm. However, storm events did not significantly impact the regular FIB monitoring. FIB removals by primary and secondary treatment were significantly correlated with FIB densities in influent wastewater; however, meteorological conditions also influenced the removal of FIB.

Influence of resuspension on the fate of fecal indicator bacteria in large-scale flumes mimicking an oligotrophic river

In this study, large-scale flume systems simulating an oligotrophic river were used to explore the fate and transport of the fecal indicator bacteria (FIB) Escherichia coli and enterococci following a combined sewer overflow (CSO). Specifically, the removal pattern of FIB from the water column was examined as well as deposition onto the flume bed. Finally, the impact that a sudden increase in bed shear stress has on FIB in the water column was investigated. The large-scale flumes utilized in this study proved extremely useful for our investigations as they very closely approximated conditions within the Isar River (Munich, Germany). By using both natural substratum and fresh river water, as well as a flow velocity of nearly 1 m s−1 at a water depth of roughly 0.5 m, shear stresses typical of the Isar River (9 N m−2) were achieved. As a result, scaling effects were appreciably reduced. In our flume system, UV inactivation played only a minimal role in overall FIB removal. Therefore, we were able to more precisely investigate other mechanisms which result in FIB removal from the water column. From the two standard FIB removal experiments following a CSO, the removal rate coefficient (k) of 0.2 h−1 was identified for both E. coli and enterococci in the water column. An increase in the bed shear stress led to more than a 150% rise in total suspended solid (TSS) levels in the water column. These elevated TSS levels (≈50 mg l−1) increased the persistence of suspended FIB in the water column by 20 h (k = 0.05 h−1). This indicates that higher TSS loads resulting from resuspended bed sediments can significantly expand the area that is impacted by a CSO event. At lower TSS loads (<20 mg l−1) deposition onto the flume bed did not contribute significantly to FIB removal from the water column. Any deposition which did occur did not result in a net accumulation of culturable FIB in the benthic biofilm.

Engineering Solutions to Improve the Removal of Fecal Indicator Bacteria by Bioinfiltration Systems during Intermittent Flow of Stormwater

Bioinfiltration systems facilitate the infiltration of urban stormwater into soil and reduce high flow events and flooding. Stormwater carries a myriad of pollutants including fecal indicator bacteria (FIB). Significant knowledge gaps exist about the ability of bioinfiltration systems to remove and retain FIB. The present study investigates the ability of model, simplified bioinfiltration systems containing quartz sand and iron oxide-coated quartz sand (IOCS) to remove two FIB (Enterococcus faecalis and Escherichia coli) suspended in synthetic stormwater with and without natural organic matter (NOM) as well as the potential for accumulated FIB to be remobilized during intermittent flow. The experiments were conducted in two phases: (1) the saturated columns packed with either sand or IOCS were contaminated by injecting stormwater with bacteria followed by injection of sterile stormwater and (2) the contaminated columns were subjected to intermittent infiltration of sterile stormwater preceded by a pause during which columns were either kept saturated or drained by gravity. During intermittent flow, fewer bacteria were released from the saturated column compared to the column drained by gravity: 12% of attached E. coli and 3% of attached Ent. faecalis were mobilized from the drained sand column compared to 3% of attached E. coli and 2% attached Ent. faecalis mobilized from the saturated sand column. Dry and wet cycles introduce moving air-water interfaces that can scour bacteria from grain surfaces. During intermittent flows, less than 0.2% of attached bacteria were mobilized from IOCS, which bound both bacteria irreversibly in the absence of NOM. Addition of NOM, however, increased bacterial mobilization from IOCS: 50% of attached E. coli and 8% of attached Ent. faecalis were released from IOCS columns during draining and rewetting. Results indicate that using geomedia such as IOCS that promote irreversible attachment of bacteria, and maintaining saturated condition, could minimize the mobilization of previous attached bacteria from bioinfiltration systems, although NOM may significantly decrease these benefits.

Modeling of slow sand filtration for disinfection of secondary clarifier effluent

Due to increasing water scarcity, appropriate technologies are needed for disinfection of wastewater to enable safe reuse. Research on hygienisation of secondary effluent using slow sand filters is very limited but promising with removal of fecal indicator bacteria of >2log-units. A quantitative description of the processes leading to bacteria removal is lacking and therefore a model was developed for E. coli removal from secondary clarifier effluent in slow sand filters. Removal was successfully simulated for sands of variable grain size distribution and under a range of hydraulic loading rates compared to data obtained at pilot-scale filters. The most important process was retention of bacteria at the “schmutzdecke” and sand surface leading to an enrichment by a factor of up to 600 compared to the surrounding bulk phase. Bacteria elimination and inactivation both in the bulk phase and the schmutzdecke can be described by a first order kinetic.

Effects of tetracycline on antibiotic resistance and removal of fecal indicator bacteria in aerated and unaerated leachfield mesocosms

Antibiotics can be present in low concentrations in domestic wastewater, but little is known about their effect on bacteria in onsite wastewater treatment systems. Mesocosms, consisting of soil-filled lysimeters representing the leachfield of a septic system under aerated (AIR) and unaerated (LEACH) conditions, were used to study the effects of tetracycline addition (5 mg L− 1) to septic tank effluent on tetracycline resistance in the fecal indicator bacteria Escherichia coli and fecal streptococci, and on their removal. The mesocosms were dosed with antibiotic for 10 days, and effects monitored for 52 days. The fraction of resistant bacteria in mesocosm drainage water relative to that in septic tank effluent, ΓRes, for E. coli ranged from 0 to 0.66 in the AIR treatment and from 0 to 3.32 in the LEACH treatment. For fecal streptococci, ΓRes ranged from 0 to 0.41 and from 0.63 to 1.06 in the AIR and LEACH treatments, respectively. No significant differences in antibiotic resistance of fecal indicator bacteria were observed among sampling dates in soil or water from either treatment. Tetracycline had no significant effect on removal of fecal indicator bacteria, which ranged from 99.9 to 100% for E. coli and from 95.9 to 100% for fecal streptococci. Our results suggest that short-term addition of tetracycline at environmentally-relevant concentrations is likely to have minimal consequences on pathogen removal from wastewater and development of antibiotic resistance among pathogenic bacteria in leachfield soil.