Removal of bacteria by filtration in planted and non-planted sand columns

Enhancing pollutant removal efficiency in urban domestic wastewater treatment through the hybrid multi-soil-layering (MSL) system: A case study in Morocco

This paper evaluates the performance and potential of a full-scale hybrid multi-soil-layering (MSL) system for the treatment of domestic wastewater for landscape irrigation reuse. The system integrates a solar septic tank and sequential vertical flow MSL and horizontal flow MSL components with alternating layers of gravel and soil-based material. It operates at a hydraulic loading rate of 250 L/m2/day. Results show significant removal of pollutants and pathogens, including total suspended solids (TSS) (97%), chemical oxygen demand (COD) (88.57%), total phosphorus (TP) (79.93%), and total nitrogen (TN) (88.49%), along with significant reductions in fecal bacteria indicators (4.21 log for fecal coliforms and 3.90 log for fecal streptococci) and the pathogen Staphylococcus sp. (2.43 log). The principal component analysis confirms the effectiveness of the system in reducing the concentrations of NH4, COD, TP, PO4, fecal coliforms, fecal streptococci, and fecal staphylococci, thus supporting the reliability of the study. This work highlights the promising potential of the hybrid MSL technology for the treatment of domestic wastewater, especially in arid regions such as North Africa and the Middle East, to support efforts to protect the environment and facilitate the reuse of wastewater for landscape irrigation and agriculture.

Shedding light on the total and active core microbiomes in slow sand filters for drinking water production

Slow sand filters (SSF) are widely used in the production of drinking water as a last barrier in the removal of pathogens. This removal mainly depends on the 'Schmutzdecke', a biofilm-like layer on the surface of the sand bed. Most previous studies focused on the total community as revealed by DNA analysis rather than on the active community, which may lead to an incorrect understanding of the SSF ecology. In the current study, we determined and compared the DNA- (total) and RNA-displayed (active) communities in the Schmutzdecke layer from 10 full-scale slow sand filters and further explored the SSF core microbiome in terms of both presence (DNA) and activity (RNA). Discrepancies were observed between the total and the active community, although there was a consistent grouping in the PCoA analysis. The DNA-displayed community may be somewhat inflated, while the RNA-displayed community could reveal low abundance (or rare) but active community members. The overall results imply that both DNA (presence) and RNA (activity) data should be considered to prevent the underestimation of organisms of functional importance but lower abundance. Microbial communities of studied mature Schmutzdecke were shaped by the influent water. Nevertheless, a core microbiome was shared by the mature Schmutzdeckes from independent filters, representing the dominant and consistent microbial community composition in slow sand filters. In the DNA samples, a total of 33 VSC families ('very strict core', with a relative abundance >0.1% and 100% prevalence) were observed across all filters. Among the RNA samples, there were 18 VSC families, including 16 families that overlapped with the DNA VSC families and 2 unique RNA VSC families. The core microbial community structure was influenced by the operational parameters, including the Schmutzdecke age and the sand size, and was less influenced by water flow. In addition, indicator organisms ('biomarkers') for the Schmutzdecke age, which show the longest duration that SSF can maintain a good operation, were observed in our study. The abundant presence of bacteria belonging to bacteriap25 and Caldilineaceae was associated with older Schmutzdeckes, revealing longer periods of stable operation performance of the filter, while the high abundance of bacteria belonging to Bdellovibrionaceae and Bryobacteraceae related to short periods of stable operation performance.

Stratification and its consequences in two constructed urban stormwater wetlands

Stratification in constructed urban stormwater wetlands is one of the fundamental physical processes that affect hydrodynamics, transport and fate of stormwater pollutants. Adverse effects of stratification include decreasing pollutant retention capacity, causing the water at lower depths to become anoxic, degrading water quality and increasing stress on the downstream aquatic communities. The current study reports on a comprehensive field monitoring program of stratification and hydrodynamics in two ice-free seasons (May - October) in two constructed urban stormwater wetlands in Calgary, Canada, with different inlet, outlet, morphometric and vegetation designs. Despite their small sizes of 0.5 and 1.2 ha and shallow water depths of 0.8 m, stratification was strong and persistent in the wetlands. The response of stratification and mixing to atmospheric forcings (e.g., air temperature, atmospheric instability, rainfall depth, wind speed) and the impact of design characteristics (inlet/outlet design, water depth, surface area and aquatic vegetation) were examined and discussed. Thermal stratification, defined as a vertical temperature gradient >1 °C/m, was found to be significantly higher (up to ten times) near the inlets and last longer (up to twice) than in the main cells and the outlet basins due to the relatively cold summer inflows. The wetland with twice the permanent water volume and surface area and half the length-to-width ratio had denser submerged aquatic vegetation, higher (by up to 2 °C) water temperature and more severe (up to eight times) thermal stratification. Strong densimetric stratification and low wind stress on the water surface caused hypoxic conditions near the bed, potentially adversely affecting water quality and downstream aquatic communities.

Effectiveness of the tropical plants Rhynchospora corymbosa and Coix lacryma-jobi in vertical flow constructed wetlands for municipal primary sewage effluent treatment

The performance of two tropical plants, Rhynchospora corymbosa L. (RC) and Coix lacryma-jobi, L (CL) in treatment of primary sewage effluent in lab-scale vertical-flow constructed wetlands (VFCW) along with no plant control wetland was investigated. A batch-flow VFCWs were operated under batch fill and drain hydraulic loading system with hydraulic retention times (HRT) of 0.5, 1, and 2 days and fill rate of 8 L/day. Removal of solids, organics, nutrients, and pathogens were monitored. The volumetric contaminant removal rates were best described by 1st order kinetics except for ammonia and phosphate, which was best described by Stover-Kincannon kinetics. Influent TSS, PO43-, COD, BOD5, and total coliform concentration were low but high in NH4+ concentration. CL was better in nutrient removal as HRT increases compared to RC. RC was more efficient at TSS, turbidity, and organics removal. Pathogen removal was independent of plant type but HRT. Solids and organic removal were lower in CL planted CWs due to preferential flow paths created by their bulky root. CL planted CWs removed more nutrients followed by RC planted CWs and then no-plant control CWs. The results of these tests demonstrate that both CL and RC are suitable for the treatment of municipal wastewater in VFCW system.

Characteristic of KMnO4-modified corn straw biochar and its application in constructed wetland to treat city tail water

Biochar prepared from straw as constructed wetland (CW) substrate reduces straw pollution and simultaneously promotes the wastewater treatment efficiency of CW. In order to further analyze the pollutant removal mechanism of KMnO₄-modified biochar substrate, the KMnO₄-modified biochar was characterized. The experiment on city tail water treatment by CW with biochar was analyzed. The research showed that the surface property improvement on KMnO₄ (0.1 mol/L)-modified biochar was the most obvious. The biochar modified by 0.1 mol/L KMnO₄ increased the SSA and the number of oxygen functional groups and alcohol hydroxyl. KMnO₄-modified biochar improved the removal efficiency of NO₃^--N in CW. KMnO₄-modified biochar substrate with plants improved the TP removal efficiency (about 45%). KMnO₄ as modifier reduced the influence of biochar on electrical conductivity tracing experiment. This study will improve the utilization value of straw and the removal efficiency of CW.

Towards Effective, Sustainable Solution for Hospital Wastewater Treatment to Cope with the Post-Pandemic Era

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has spread across the globe since the end of 2019, posing significant challenges for global medical facilities and human health. Treatment of hospital wastewater is vitally important under this special circumstance. However, there is a shortage of studies on the sustainable wastewater treatment processes utilized by hospitals. Based on a review of the research trends regarding hospital wastewater treatment in the past three years of the COVID-19 outbreak, this review overviews the existing hospital wastewater treatment processes. It is clear that activated sludge processes (ASPs) and the use of membrane bioreactors (MBRs) are the major and effective treatment techniques applied to hospital wastewater. Advanced technology (such as Fenton oxidation, electrocoagulation, etc.) has also achieved good results, but the use of such technology remains small scale for the moment and poses some side effects, including increased cost. More interestingly, this review reveals the increased use of constructed wetlands (CWs) as an eco-solution for hospital wastewater treatment and then focuses in slightly more detail on examining the roles and mechanisms of CWs' components with respect to purifying hospital wastewater and compares their removal efficiency with other treatment processes. It is believed that a multi-stage CW system with various intensifications or CWs incorporated with other treatment processes constitute an effective, sustainable solution for hospital wastewater treatment in order to cope with the post-pandemic era.

Bio-removal of emerging pollutants by advanced bioremediation techniques

This review highlights the relevance of bioremediation techniques for the removal of emerging pollutants (EPs). The EPs are chemical or biological pollutants that are not currently monitored or regulated by environmental authorities, but which can enter the environment and cause harmful effects to the environment and human health. In recent times, an ample range of EPs have been found in water bodies, where they can unbalance ecosystems and cause negative effects on non-target species. In addition, some EPs have shown high rates of bioaccumulation in aquatic species, thus affecting the safety and quality of seafood. The negative impacts of emerging pollutants, their wide distribution in the environment, their bioaccumulation rates, and their resistance to wastewater treatment plants processes have led to research on sustainable remediation. Remediation techniques have been recently directed to advanced biological remediation technologies. Such technologies have exhibited numerous advantages like in-situ remediation, low costs, eco-friendliness, high public acceptance, and so on. Thus, the present review has compiled the most recent studies on bioremediation techniques for water decontamination from emerging pollutants to extend the current knowledge on sustainable remediation technologies. Biological emerging contaminants, agrochemicals, endocrine-disrupting chemicals, and pharmaceutical and personal care products were considered for this review study, and their removal by bioremediation techniques involving plants, bacteria, microalgae, and fungi. Finally, further research opportunities are presented based on current challenges from an economic, biological, and operation perspective.

Removal of bacterial indicators in on-site two-stage multi-soil-layering plant under arid climate (Morocco): prediction of total coliform content using K-nearest neighbor algorithm

This study aims to evaluate and monitor the efficacy of a full-scale two-stage multi-soil-layering (TS-MSL) plant in removing fecal contamination from domestic wastewater. The TS-MSL plant under investigation consisted of two units in series, one with a vertical flow regime (VF-MSL) and the other with a horizontal flow regime (HF-MSL). Furthermore, this study attempts to see whether linear model (LM) and K-nearest neighbor (KNN) model can be used to predict total coliform (TC) removal in the TS-MSL system. For 24 months, the TS-MSL system was monitored, with bimonthly measurements recorded at the inlet and outlet of each compartment. Obtained results show removal of 85% of COD, 67% of TP, 27% of TN, and 3 log units of coliforms with good system stability. Thus, the effluent meets the Moroccan water quality code for reuse in the irrigation of green spaces. In addition, as compared to LM, the KNN model (R² = 0.988) may be considered as an effective method for predicting TC removal in the TS-MSL system. Finally, sensitivity analysis has shown that TC and dissolved oxygen level in the influent were the most influential parameters for predicting TC removal in the TS-MSL system.

Internalisation of Salmonella spp. by Typha latifolia and Cyperus papyrus in vitro and implications for pathogen removal in Constructed Wetlands

ABSTRACTFreshwater contamination by enteric pathogens is implicated in the high frequency of diarrhoeal diseases in low to middle income countries, typically due to poor wastewater management. Constructed Wetlands are a cost-effective and sustainable alternative to conventional/mechanical treatment technologies, but the pathogen removal mechanisms in Constructed Wetlands are not fully understood. This study investigated for the first time the internalisation of Salmonella spp. by Typha latifolia and Cyperus papyrus in hydroponic microcosms. Presence of Salmonella spp. within roots, rhizomes and shoots was assayed using agar-based methods over a period of 12 days. Concentration of Salmonella spp. in growth media showed 2.7 and 4.8 log unit reduction with T. latifolia and C. papyrus, respectively, and 1.8 and 6.0 log unit in unplanted units. Salmonella spp. was recovered from root and rhizome tissues of T. latifolia (up to 4.4 logCFU/g) and C. papyrus (up to 3.4 logCFU/g), and the bacteria were highly concentrated in the epidermis and cortex. However, Salmonella spp. was not detected in the stems and leaves of the two plant species. The present study demonstrates for the first time that these macrophytes internalise cells of Salmonella spp., which could be one pathogen removal mechanism employed by wetland plants.

Mechanistic understanding of the pollutant removal and transformation processes in the constructed wetland system

Constructed wetland systems (CWs) are biologically and physically engineered systems to mimic the natural wetlands which can potentially treat the wastewater from the various point and nonpoint sources of pollution. The present study aims to review the various mechanisms involved in the different types of CWs for wastewater treatment and to elucidate their role in the effective functioning of the CWs. Several physical, chemical, and biological processes substantially influence the pollutant removal efficiency of CWs. Plants species Phragmites australis, Typha latifolia, and Typha angustifolia are most widely used in CWs. The rate of nitrogen (N) removal is significantly affected by emergent vegetation cover and type of CWs. Hybrid CWs (HCWS) removal efficiency for nutrients, metals, pesticides, and other pollutants is higher than a single constructed wetland. The contaminant removal efficiency of the vertical subsurface flow constructed wetlands (VSSFCW) commonly used for the treatment of domestic and municipal wastewater ranges between 31% and 99%. Biochar/zeolite addition as substrate material further enhances the wastewater treatment of CWs. Innovative components (substrate materials, plant species) and factors (design parameters, climatic conditions) sustaining the long-term sink of the pollutants, such as nutrients and heavy metals in the CWs should be further investigated in the future. PRACTITIONER POINTS: Constructed wetland systems (CWs) are efficient natural treatment system for on-site contaminants removal from wastewater. Denitrification, nitrification, microbial and plant uptake, sedimentation and adsorption are crucial pollutant removal mechanisms. Phragmites australis, Typha latifolia, and Typha angustifolia are widely used emergent plants in constructed wetlands. Hydraulic retention time (HRT), water flow regimes, substrate, plant, and microbial biomass substantially affect CWs treatment performance.

Removal of Pathogens in Onsite Wastewater Treatment Systems: A Review of Design Considerations and Influencing Factors

Conventional onsite wastewater treatment systems (OWTSs) could potentially contribute to the transmission of infectious diseases caused by waterborne pathogenic microorganisms and become an important human health concern, especially in the areas where OWTSs are used as the major wastewater treatment units. Although previous studies suggested the OWTSs could reduce chemical pollutants as well as effectively reducing microbial contaminants from onsite wastewater, the microbiological quality of effluents and the factors potentially affecting the removal are still understudied. Therefore, the design and optimization of pathogen removal performance necessitate a better mechanistic understanding of the hydrological, geochemical, and biological processes controlling the water quality in OWTSs. To fill the knowledge gaps, the sources of pathogens and common pathogenic indicators, along with their major removal mechanisms in OWTSs were discussed. This review evaluated the effectiveness of pathogen removal in state-of-art OWTSs and investigated the contributing factors for efficient pathogen removal (e.g., system configurations, filter materials, environmental and operational conditions), with the aim to guide the future design for optimized treatment performance.

Organics and nutrients removal in vertical flow wetlands: loading fluctuation and alternative media

Two wetland systems (conventional and structurally modified) were studied for the removal of organics and nutrients from municipal wastewater. Each system consisted of three vertical flow (VF) wetlands, which were filled with agricultural, construction waste materials and planted with Phragmites australis and Canna indica. The wetland units were operated under constant and consecutive shock hydraulic load (HL). Input nutrients and organics load across the wetland units ranged between 4.0-116.0 g N/m²d, 0.5-23.0 g P/m²d, 1.0-527.0 g biochemical oxygen demand (BOD)/m²d and 16.0-686.0 g chemical oxygen demand (COD)/m²d. Nitrification and organic carbon availability controlled nitrogen (N) removals in first and third stage VF wetlands, respectively, during constant load phase; organics removals were influenced by dissolved oxygen concentration of municipal wastewater. Second stage VF wetlands (of both systems) were inefficient in terms of COD removals during shock load periods, which were counter-balanced by first and third stages. First stage VF wetlands achieved higher N removal rates than following stages during shock load periods. Wetland maturation provided a buffer against substantial HL increment and sharp input load decrease in latter shock and recovery phases, respectively. Agricultural waste (sugarcane bagasse) provided carbon to support denitrification; construction materials (recycled brick and crushed mortar) removed phosphorus (P) from wastewater through adsorption. Coliform removal in VF wetlands was achieved through media filtration. Structurally modified system achieved higher removals than the conventional system. BOD, COD, total nitrogen and NH₄-N removal percentage across two systems ranged between 76-79%, 59-63%, 73-77% and 90-95%, respectively. In general, this study enlightens potential application of appropriate waste materials for wastewater treatment.

A constructed wetland system with aquatic macrophytes for cleaning contaminated runoff/storm water from urban area in Florida

A community of aquatic macrophytes has an important role in reducing nutrient load and organic and inorganic contaminants in storm/runoff water. However, minimal information is available regarding the efficiency of constructed wetlands for cleaning runoff water from urban areas, especially in the tropical and subtropical regions. This study investigated the effectiveness of constructed wetland integrated with aquatic macrophytes for removal of chemical and microbial contaminants in the storm/runoff water from the urban areas. Water samples were monthly collected in the constructed wetland from the inlet of storm/runoff water, middle and outlet of discharge, and analyzed for physical and chemical properties, concentrations of nutrients, metals, and fecal coliform (FC) during the period of November, 2016 to April, 2018 in St. Lucie county, Florida, USA. The dominant plant species in the constructed wetland included cattail (Typha latifolia), waterthyme (Hydrilla verticillata) and water hyacinth (Eichhornia crassipes), and periphyton filamentous algae (Spirogyra). The improvement of pH and electrical conductivity (EC) was not obvious, but the concentration of total suspended solids was significantly reduced. This system was effective in the removal of fecal coliform (by 68%) and particulate phosphorus (P, 72%), followed by total P (42%) and N (35%). Concentrations of metallic pollutants including cadmium (Cd), lead (Pb), chromium (Cr), and copper (Cu) were mostly below the detection limit (<1 ppb) except for zinc (Zn), of which concentration was reduced by 23%. The removal of FC was consistently effective all the year round, whereas the removal of total N, P and particulate-P was effective in spring and summer, and less in autumn and winter. These results indicate that constructed wetland with a natural aquatic plant community can effectively reduce the loads of nutrients, metals, and fecal coliforms in water column. Regular harvest of aquatic macrophytes communities and collecting litters may further improve the system efficiency for cleaning storm water from urban areas.

Implementation of Floating Treatment Wetlands for Textile Wastewater Management: A Review

The textile industry is one of the most chemically intensive industries, and its wastewater is comprised of harmful dyes, pigments, dissolved/suspended solids, and heavy metals. The treatment of textile wastewater has become a necessary task before discharge into the environment. The textile effluent can be treated by conventional methods, however, the limitations of these techniques are high cost, incomplete removal, and production of concentrated sludge. This review illustrates recent knowledge about the application of floating treatment wetlands (FTWs) for remediation of textile wastewater. The FTWs system is a potential alternative technology for textile wastewater treatment. FTWs efficiently removed the dyes, pigments, organic matter, nutrients, heavy metals, and other pollutants from the textile effluent. Plants and bacteria are essential components of FTWs, which contribute to the pollutant removal process through their physical effects and metabolic process. Plants species with extensive roots structure and large biomass are recommended for vegetation on floating mats. The pollutant removal efficiency can be enhanced by the right selection of plants, managing plant coverage, improving aeration, and inoculation by specific bacterial strains. The proper installation and maintenance practices can further enhance the efficiency, sustainability, and aesthetic value of the FTWs. Further research is suggested to develop guidelines for the selection of right plants and bacterial strains for the efficient remediation of textile effluent by FTWs at large scales.

The influence mechanism of bioclogging on pollution removal efficiency of vertical flow constructed wetland

The effect of change of hydraulic characteristic and microbial community on pollution removal efficiency of the infiltration systems in the bioclogging development process remain poorly understood. In this study, therefore, the pollutant removal as a response to hydraulic conductivity reduction and the change of diversity and structure of microbial communities in vertical flow constructed wetlands (VFCWs) was investigated. The results indicated that the richness and diversity of the bacterial communities in the columns at different depths were decreased, and the microbial communities of the genus level were changed in the process of bioclogging. However, the variation of microbial communities has a low impact on the purification performance of VFCWs because the abundance of function groups, respiratory activity, and degradation potentiality of microorganisms remain steady or even get improved in the columns after bioclogging. On the contrary, the hydraulic efficiency of VFCWs decreased greatly by 16.9%, 9.9%, and 57.1% for VFCWs filled with zeolite (Column I), gravel (Column II), and ceramsite (Column III), respectively. The existence of short-circuiting and dead zones in the filter media cause the poor pollution removal efficiency of VFCWs due to the short contact time and decrease of oxygenation renewal, as well as low activity in the dead zone.

Rapid plant responses following relocation of a constructed floating wetland from a construction site into an urban stormwater retention pond

This study compared plant growth, nutrient partitioning and total nutrient uptake by tall sedge (Carex appressa) plants in large-scale Constructed Floating Wetlands (CFWs). Two CFWs with a total area of 2088 m² were installed in a 2.6 ha man-made urban lake to treat stormwater runoff during the construction phase of a 45-ha residential development. After 12 months of operation, parts of the CFWs, with a total area of 147 m², were removed from the urban lake and relocated into a well-established 0.127-ha stormwater retention pond at another site. Biomass and nutrient concentrations of C. appressa shoots above the floating mat and roots below the mat were analysed at both sites 12, 16 and 25 months after initial planting. Plants at the urban lake maintained an extensive root network but there was no increase in total plant biomass at 16 and 25 months after planting. In contrast, the relocated plants in the stormwater pond showed extensive shoot growth but a significant decline in root biomass. C. appressa at the urban lake removed and sequestered 1.00 ± 1.04 g m^-2 N, 0.11 ± 0.07 g m^-2 P and 1.03 ± 0.81 g m^-2 K while plants at the pond removed 11.20 ± 2.29 g m^-2 N, 1.37 ± 0.26 g m^-2 P and 16.13 ± 2.88 g m^-2 K during 12 and 25 months after planting. This study demonstrated that C. appressa adapted rapidly to changes in nutrient availability. The implications are interesting as nutrient levels can be low in constructed lakes during the initial phase of urban developments but can increase rapidly as the development progresses. The study demonstrated multiple benefits of CFWs for stormwater treatment during the early construction stages of an urban development and the potential benefits of relocating and establishing CFWs in existing stormwater retention ponds and lakes.

New prebiotic chemistry inspired filter media for stormwater/greywater disinfection

Greywater and stormwater have received significant attention due to increasing water scarcity. Passive filtration such as biofiltration has been a popular treatment method with its low energy input and environmental friendliness. However, pathogen removal capacity needs improvement to achieve safe water quality. In this study, a prebiotic chemistry inspired copolymer based on aminomalononitrile and 3,4,5-trihydroxybenzaldehyde (AMNT30) was introduced to develop antimicrobial media for passive filtration. The AMNT30 polymer provided an adhesive coating on zeolite substrates following a spontaneous polymerisation process at room temperature. AMNT30 coated media were investigated for metal loading capacity, surface morphology, E. coli removal and metal leaching after filtration of different water sources (i.e. stormwater, greywater, and deionised water) at low/high conductivity. The coating enhanced metal ion loading on the surface and demonstrated that >8 log reduction of E. coli can be achieved for silver loaded materials compared to a 1 log reduction for copper loaded materials. The coating also increased the stability of the metals on the media irrespective of inflow characteristics. This study provided the first example using AMNT30 to create antimicrobial water purification media. It is expected that this technology will find applications in the water treatment industry.

Constructed wetland for wastewater reuse: Role and efficiency in removing enteric pathogens

Water stress has become a perennial concern in most of the developing countries due to rapid urbanization and population growth. As the growing population requires more fresh water and better ways for wastewater disposal, the demand for wastewater reclamation has increased drastically in recent years. Wastewater, either raw or treated, is being widely used for agricultural irrigation in developing countries, which cause a serious threat to human health mainly because of its pathogenic content. One of the alternative methods to treat wastewater and make it reusable for agricultural irrigation is to implement constructed wetland (CW); a sustainable and cost-effective technology that is applicable for the elimination of both pollutants and pathogens from wastewater. Despite its wide application, the role of macrophytes that form an integral part of CW and specific mechanisms involved in pathogen removal by them is still barely understood due to complexities involved and influencing factors. This has, therefore, attracted various scientific studies to reveal further functional mechanisms involved in vegetated CW to increase its proficiencies. This review paper illustrates the comparative studies of different CW and their pathogen removal efficiencies with major emphasis on macrophytes involved and factors influencing related mechanism. Further, the paper also covers detailed information on the enteric pathogens present in wastewater and the associated health risks involved in its reuse. The ultimate objective is to further clarify the role of CW in enteric pathogen removal and its efficiency for wastewater purification in perspective with safe reuse in agriculture.

Agro-industrial residues as a unique support in a sand filter to enhance the bioactivity to remove microcystin-Leucine aRginine and organics

In the past, the versatility of a biosand filter has been successfully checked to counter suspended solids, metals, dissolved organic carbon (DOC), coliforms and other water quality parameters (WQPs) from the drinking water sources. In this study, cyanotoxin in the form of microcystin-LR (MC-LR) along with above-mentioned WQPs including nitrate, nitrite, and ammonia are analyzed for their removal using agro-residue based biosand filters (ARSFs) for 49 days (7 cycles). Three different agro-residue materials (ARMs) viz. deinking sludge (DSF), hemp fiber (HFF) and paper-pulp dry sludge (PPF) were used as the support material (top 5 cm) along with sand (49 cm) as the primary filter media to enhance the overall bioactivity. This enhancement in bioactivity is hypothesized to remove more MC-LR, DOC, coliform along with efficient nitrification/denitrification. Native bacterial community isolated from the filtration unit of a drinking water treatment plant (Chryseobacterium sp. and Pseudomonas fragi = X) along with the MC-LR-degrader: Arthrobacter ramosus (which was screened as the best biofilm-former among two other MC-LR-degraders tested) were used to inoculate the filters (all three ARSFs). Overall, DSF performed the best among all the ARSFs when compared to the sand filter (SFI) inoculated with the same bacterial strains (A + X). An increase in the bioactivity for ARSFs, particularly DSF was evident from the DOC removal (44 ± 11%, 15% more than SFI), coliform removal (92.7 ± 12.8%, 24% more than SFI), MC-LR removal (87 ± 14%, 13% more than SFI) and an effective nitrification/denitrification, reducing ammonia, nitrate and nitrite level to below guideline values. Toxic assessment using bioindicator (Rhizobium meliloti) revealed safe filter water only in case of DSF.

Presence of bacteria and bacteriophages in full-scale trickling filters and an aerated constructed wetland

Aerated Constructed Wetlands are a state-of-the-art design that provides a different physical and chemical environment (compared to traditional passive wetland designs) for the wastewater treatment processes and, thus, may have different pathogen removal characteristics. In order to establish the fate of bacterial and viral indicators, a field study was carried out at a Sewage Treatment Works (STW) in the UK (serving 20,000 pe). The STW consists of primary and secondary sedimentation tanks and trickling filters (TF) as the biological stage. A large (1,160 m²) pilot aerated Vertical Flow Constructed Wetland (AVFCW) was constructed at the STW as tertiary stage receiving ¼ of the total flow rate, i.e., 1250 m³/day. Effluent quality of the AVFCW complied with national and international standards for environmental discharge and reuse. For the first time, two sets of bacterial (Faecal coliforms, E.coli and intestinal enterococci) and viral indicators (Somatic coliphages, F-RNA specific bacteriophages and human-specific B. fragilis GB124 phages) were simultaneously investigated in an AVFCW and TF. High elimination rates were detected (up to 3.7 and 2.2 log reduction for bacteria indicators and phages, respectively) and strong correlations between the two sets were found. The superior efficiency of the aerated Constructed Wetlands in microbiological contamination removal compared to passive wetland systems was established for the first time, which may have implications for process selection for wastewater reuse. This field study therefore provides new evidence on the fate of bacteriophages and a first indication of their potential use for performance evaluation in TF and aerated Constructed Wetlands. It also demonstrates that the combination of TF with aerated constructed wetlands could be a novel and effective treatment scheme for new STW or for the upgrade of existing STW.

Potential for CSO treatment with horizontal flow constructed wetlands: influence of hydraulic load, plant presence and loading frequency

This study aimed at analysing the performance of horizontal subsurface flow constructed wetlands (CWs) to treat combined sewer overflow (CSO). Four horizontal subsurface flow CWs, organized in two groups (A and B) each with a planted (Phragmites australis) and a non-planted bed, were loaded with simulated CSO, with group B receiving twice the hydraulic load of group A. Beds were monitored for pH, dissolved oxygen, conductivity, redox potential, chemical oxygen demand (COD), total suspended solids (TSS) and enterococci. Porosity variations were also estimated. Monitoring was conducted during spring and wintertime, with regular and irregular loading frequencies. Results showed an average treatment efficiency of 90-100 % for TSS, 60-90 % for COD and 2-6 log for enterococci. Removal rates were especially relevant in the first 24 h for COD and TSS. TSS and enterococci removal did not exhibit the influence of macrophytes or the applied hydraulic load while COD's removal efficiency was lower in the higher load group and in planted beds.

Sanitation in constructed wetlands: A review on the removal of human pathogens and fecal indicators

Removal of human pathogens from wastewater is a critical factor with linkage to human health. Constructed Wetlands (CWs) are environmental friendly ecosystems that are applicable not only for chemical pollution control, but also for the reduction of pathogens from wastewater. Yet the knowledge on the fate and removal of such indicator bacteria in CWs is still not sufficient due to the complexity of removal mechanisms and influencing factors. This review serves to provide a better understanding of this state-of-the-art technology, which is necessary for further investigations and design development. The fecal indicator bacteria in CWs mainly come from three sources, namely, influent wastewaters, regrowth within the CWs, and animal activities. The properties of microbial contamination vary depending on the different sources. The removal of pathogens is a complex process that is influenced by operational parameters such as hydraulic regime and retention time, vegetation, seasonal fluctuation, and water composition. The most frequent and well-validated removal mechanisms include natural die-off due to starvation or predation, sedimentation and filtration, and adsorption. The concentration of the main fecal indicator bacteria in the effluent was found to be exponentially related to the loading rate. Generally, horizontal subsurface flow CWs have better reduction capacity than free water surface flow CWs, and hybrid wetland systems were found to be the most efficient due to a longer retention time. Further improvement of fecal indicator bacteria removal in CWs is needed, however, levels in CW effluents are still higher than most of the regulation standards for reuse.

The predatory bacterium Bdellovibrio bacteriovorus aspartyl-tRNA synthetase recognizes tRNAAsn as a substrate

The predatory bacterium Bdellovibrio bacteriovorus preys on other Gram-negative bacteria and was predicted to be an asparagine auxotroph. However, despite encoding asparaginyl-tRNA synthetase and glutaminyl-tRNA synthetase, B. bacteriovorus also contains the amidotransferase GatCAB. Deinococcus radiodurans, and Thermus thermophilus also encode both of these aminoacyl-tRNA synthetases with GatCAB. Both also code for a second aspartyl-tRNA synthetase and use the additional aspartyl-tRNA synthetase with GatCAB to synthesize asparagine on tRNA^Asn. Unlike those two bacteria, B. bacteriovorus encodes only one aspartyl-tRNA synthetase. Here we demonstrate the lone B. bacteriovorus aspartyl-tRNA synthetase catalyzes aspartyl-tRNA^Asn formation that GatCAB can then amidate to asparaginyl-tRNA^Asn. This non-discriminating aspartyl-tRNA synthetase with GatCAB thus provides B. bacteriovorus a second route for Asn-tRNA^Asn formation with the asparagine synthesized in a tRNA-dependent manner. Thus, in contrast to a previous prediction, B. bacteriovorus codes for a biosynthetic route for asparagine. Analysis of bacterial genomes suggests a significant number of other bacteria may also code for both routes for Asn-tRNA^Asn synthesis with only a limited number encoding a second aspartyl-tRNA synthetase.

Pollutant removal from municipal wastewater employing baffled subsurface flow and integrated surface flow-floating treatment wetlands

This article reports pollutant removal performances of baffled subsurface flow, and integrated surface flow-floating treatment wetland units, when arranged in series for the treatment of municipal wastewater in Bangladesh. The wetland units (of the hybrid system) included organic, inorganic media, and were planted with nineteen types of macrophytes. The wetland train was operated under hydraulic loading fluctuation and seasonal variation. The performance analyses (across the wetland units) illustrated simultaneous denitrification and organics removal rates in the first stage vertical flow wetland, due to organic carbon leaching from the employed organic media. Higher mean organics removal rates (656.0 g COD/(m(2)·day)) did not completely inhibit nitrification in the first stage vertical flow system; such pattern could be linked to effective utilization of the trapped oxygen, as the flow was directed throughout the media by the baffle walls. Second stage horizontal flow wetland showed enhanced biodegradable organics removal, which depleted organic carbon availability for denitrification. The final stage integrated wetland system allowed further nitrogen removal from wastewater, via nutrient uptake by plant roots (along with nitrification), and generation of organic carbon (by the dead macrophytes) to support denitrification. The system achieved higher E. coli mortality through protozoa predation, E. coli oxidation, and destruction by UV radiation. In general, enhanced pollutant removal efficiencies as demonstrated by the structurally modified hybrid wetland system signify the necessity of such modification, when operated under adverse conditions such as: substantial input organics loading, hydraulic loading fluctuation, and seasonal variation.

Polishing domestic wastewater on a subsurface flow constructed wetland: organic matter removal and microbial monitoring

Microbial monitoring of constructed wetlands (CWs) treating domestic wastewater is generally scarce, despite the need of more knowledge about its biocenosis. The sanitation quality of a wastewater treated in a CW is a crucial aspect, mainly when the receiving water body is used as a swimming and/or recreation area. The present study was carried out in a horizontal subsurface flow CWplanted with Phragmites australis receiving pre-treated domestic wastewater (mean flow 50 m3 day(-1)), from a population of about 300 inhabitants. The monitoring programme undertaken during the first year operation, revealed removal efficiencies of 61% BOD5, 44% COD, and 65% TSS for inlet water with ca. 90 mg L(-1) BOD5, 157 mg L(-1) COD, and 17 mg L(-1) TSS. Total Coliform (TC) and Faecal Coliform (FC) bacteria were removed from wastewater (mean inlet values of 5 x 10(6) CFU 100 mL(-1) TC and of 9 x 10(5) CFU 100 mL(-1) FC), with efficiencies of 92 and 97%, respectively. The dynamics of microbial communities established in the system assessed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), had revealed a high bacterial diversity within the system, with no relevant differences in composition at the CW inlet and outlet but exhibiting temporal differences in bacterial communities.

Enhanced denitrification and organics removal in hybrid wetland columns: comparative experiments

This study investigated three lab-scale hybrid wetland systems with traditional (gravel) and alternative substrates (wood mulch and zeolite) for removing organic, inorganic pollutants and coliforms from a synthetic wastewater, in order to investigate the efficiency of alternative substrates, and monitor the stability of system performance. The hybrid systems were operated under controlled variations of hydraulic load (q, 0.3-0.9 m3/m2 d), influent ammoniacal nitrogen (NH4-N, 22.0-80.0 mg/L), total nitrogen (TN, 24.0-84.0 mg/L) and biodegradable organics concentration (BOD5, 14.5-102.0 mg/L). Overall, mulch and zeolite showed promising prospect as wetland substrates, as both media enhanced the removal of nitrogen and organics. Average NH4-N, TN and BOD5 removal percentages were over 99%, 72% and 97%, respectively, across all three systems, indicating stable removal performances regardless of variable operating conditions. Higher Escherichia coli removal efficiencies (99.9%) were observed across the three systems, probably due to dominancy of aerobic conditions in vertical wetland columns of the hybrid systems.

Identification of protozoa in dairy lagoon wastewater that consume Escherichia coli O157:H7 preferentially

Escherichia coli O157:H7 (EcO157), an agent of life threatening hemolytic-uremic syndrome, resides in ruminants and is released in feces at numbers as high as 10 million cells/gram. EcO157 could survive in manure for as long as 21 months, but we observed a 90% decrease in cells of an outbreak strain of EcO157 within half a day in wastewater from dairy lagoons. Although chemical, environmental and biological factors may be responsible for this decrease, we observed an 11-fold increase in native protozoa when wastewater was re-inoculated with 2×10⁷ cells of EcO157/mL. These protozoa engulfed the green fluorescent protein labeled EcO157 within 2 hours after inoculation, but expelled vacuoles filled with live EcO157 cells within 3 days into surrounding wastewater, whereas other protozoa retained the EcO157-filled vacuoles for 7 days. EcO157 was not detected by confocal microscopy either inside or outside protozoa after 7 days. Mixed cultures of protozoa enriched from wastewater consumed EcO157 preferentially as compared to native aerobic bacteria, but failed to eliminate them when EcO157 cells declined to 10⁴/mL. We isolated three protozoa from mixed cultures and typed them by 18S sequencing as Vorticella microstoma, Platyophyra sp. and Colpoda aspera. While all three protozoa internalized EcO157, only Platyophyra and Colpoda acted as predators. Similar to mixed cultures, these protozoa failed to eliminate EcO157 from PBS containing no other supplemental nutrients or prey. However, spiking PBS with cereal grass medium as nutrients induced predation of EcO157 by Platyophyra sp. after 3 days or enhanced predation by Colpoda after 5 days. Therefore, attempts to enrich protozoa to decrease EcO157 from dairy lagoons, may correspond to an increase in protozoa similar to Vorticella and possibly facilitate transport of bacterial pathogens to food crops grown in proximity.

Microbial population and activity in wetland microcosms constructed for improving treated municipal wastewater

The idea of using constructed wetlands for the treatment and improving of wastewater emerged in the second half of the last century. Despite relatively wide use of this environmentally friendly technology, relatively little is known about the microbial populations involved in biotransformation and removal of contaminants in this system. The aim of the current study was to investigate the assembly and function of microbial populations in vertical-flow constructed wetland microcosms designed to improve the quality of wastewater after activated sludge treatment. Also, the performance of 3-year-old wetland ponds was investigated. Even though the quality of the influent water was relatively high, improvement in water parameters such as coliform level, ammonia concentration, BOD, and TSS was observed. The performance of the wetland ponds was comparable to that of the microcosms. The microbial community composition of the biofilm formed on the surface of gravel particles in vegetated and plant-free microcosms was studied by denaturing gradient gel electrophoresis (DGGE) and sequencing of 16S rRNA gene fragments. Highly complex bacterial diversity was observed in the biofilm. Cluster analysis of DGGE patterns demonstrated that depth within the wetland microcosm has a stronger effect on microbial community composition of the biofilm formed on wetland matrix than vegetation. Measurements of fluorescein diacetate hydrolysis activity and nitrification potential revealed that hydrolytic activity was affected by both microcosm depth and vegetation presence, whereas nitrification potential was mostly influenced by depth. Resolving the bacterial assemblage of wetland biofilm, which often is considered a black box, will help to understand the interactions involved in the development of diverse and mature biofilm and its function.

Nutrient removal as a function of benzene supply within vertical-flow constructed wetlands

The role of benzene, macrophytes and temperature in terms of nutrient removal within constructed wetlands is unknown. Therefore, a research study over approximately 30 months was conducted to assess the potential of vertical-flow constructed wetlands to treat nutrients and to examine the effect of benzene concentration, presence of Phragmites australis (Cav.) Trin. ex Steud (common reed), and temperature control on nutrient removal. Experimental wetlands removed between 72% and 90% of benzene at an influent concentration of 1000 mg L(-1). A statistical analysis indicated that benzene is linked to increased effluent chemical oxygen demand and biochemical oxygen demand concentrations. However, there was no significant relationship between benzene treatment and both nitrogen and phosphorus removal. Phragmites australis played a negligible role in organic matter (chemical oxygen demand, biochemical oxygen demand, nitrogen and phosphorus) removal. Control of temperature favoured biochemical oxygen demand removal. However, no significant difference in chemical oxygen demand, and nitrogen and phosphorus removal was detected. Only the combination of the benzene and temperature variables had a significant impact on biochemical oxygen demand removal. The effluent biochemical oxygen demand concentrations in temperature-controlled benzene treatment wetlands were much lower than those located in the natural environment. However, any other combination between benzene, P. australis and the environmental control variables had no significant effect on biochemical oxygen demand, chemical oxygen demand, or nitrogen and phosphorus removal.

Polyurethane rotating disc system for post-treatment of anaerobically pre-treated sewage

The performance of polyurethane rotating discs (RBC-1) versus polystyrene rotating discs (RBC-2) for the treatment of an up-flow anaerobic sludge blanket (UASB) reactor effluent fed with domestic wastewater was investigated. Both RBC units were operated at the same organic loading rate (OLR) of 10.5 gCOD/m(2) d. and a hydraulic retention time (HRT) of 2.5 h. The residual values of COD fractions (COD(suspended), COD(colloidal) and COD(soluble)) in the treated effluent of RBC-1 and RBC-2 were similar. However, the removal efficiency of ammonia in the RBC-1 (87 +/- 4%) was significantly higher than that found for RBC-2 i.e. 24 +/- 6%. Moreover, RBC-1 achieved a substantial removal efficiency of 99.0 +/- 1% for Escherichia coli (E. coli), while RBC-2 removed 91.2 +/- 0.3%. Based on these results, optimization of RBC-1 treating UASB reactor effluent was extensively performed. The RBC-1 was operated at an OLR's of 4.0, 11 and 23 gCOD/m(2) d. The results obtained showed that increasing the OLR from 11.0 to 23.0 gCOD/m(2) d and decreasing the HRT from 2.5 to 1.25 h significantly declined the effluent quality of COD(total) and ammonia. However, the residual values of COD(total) and ammonia remained unaffected when increasing the OLR from 4.0 to 11.0 gCOD/m(2) d and by decreasing the HRT from 5 to 2.5 h. Bacteriological examination showed that the mean residual count of E. coli remained at a level of 10(4)/100 ml, in the effluent of RBC-1 independent on the imposed HRT. Accordingly, it is recommended to operate RBC-1 for treatment of anaerobically pre-treated sewage at an OLR of 11 gCOD/m(2) d and an HRT of 2.5 h. A feed-less (ammonia limitation) period of 9.0 days followed by 9.0 days feeding with high OLR of 26 gCOD/m(2) d. (raw sewage) was investigated to elaborate, if the nitrifiers of the RBC-1 are capable to convert ammonia to nitrate after totally 18 days when retuning back to the normal operating conditions. The results of the experiment clearly show a strong and immediate detrimental effect of imposing high OLR of 26 gCOD/m(2) d on the nitrification process in the nitrifying RBC unit. However, after returning back to the original OLR of 10.6 gCOD/m(2) d, the nitrification efficiency in the RBC unit was recovered within 2-3 days.

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.

Indicator microorganisms and pathogens removal function performed by copepods in constructed wetlands

Removal efficiency of indicator and pathogenic microorganisms in constructed wetlands were analyzed, and microorganisms removal function performed by copepods was determined. The results showed that the constructed wetlands effectively reduced Escherichia coli, fecal streptococci, total coliforms, and fecal coliforms, the Salmonella spp. removal efficiency was relatively low and the Clostridium perfringens removal was the least. At copepods concentrations of 3.0 x 10(2)/L, and 6.0 x 10(2)/L, high die-off rates were observed for indicator and pathogenic microorganisms compared to the control group, and indicator and pathogenic microorganisms in samples with higher concentration of copepods decreased much more rapidly than those in samples with lower concentration. These results suggest that predation by copepods is an important mechanism for the removal of bacteria in constructed wetlands.

Removal of fluoride, arsenic and coliform bacteria by modified homemade filter media from drinking water

An attempt was made to investigate the removal of fluoride, arsenic and coliform bacteria from drinking water using modified homemade filter media. Batch mode experimental study was conducted to test the efficiency of modified homemade filter for reduction of impurities under the operating condition of treatment time. The physico-chemical and biological analysis of water samples had been done before and after the treatment with filter media, using standard methods. Optimum operating treatment time was determined for maximum removal of these impurities by running the experiment for 2, 4, 6, 8, 10 and 12h, respectively. The maximum reduction of fluoride, arsenic and coliform bacteria in percentage was 85.60%, 93.07% and 100% and their residual values were 0.72 mg/l, 0.009 mg/l and 0 coliform cells/100ml, respectively after a treatment time of 10h. These residual values were under the permissible limits prescribed by WHO. Hence this could be a cheap, easy and an efficient technique for removal of fluoride, arsenic and coliform bacteria from drinking water.