Effect of organic load on phosphorus and bacteria removal from wastewater using alkaline filter materials

Improved removal performance of Gram-negative and Gram-positive bacteria in sand filtration system with arginine modified biochar amendment

Bacterial removal by sand filtration system is commonly inefficient due to the low bacterial adsorption capacity of sand. To improve the bacterial removal performance, biochar fabricated at different temperatures (400 °C, 550 °C and 700 °C) and arginine modified biochar were added into sand filtration columns as filter layers (0.5 and 1 wt%). Addition of biochar into sand columns could improve the removal efficiency for both Escherichia coli and Bacillus subtilis under both slow (4 m/day) and fast (240 m/day) filtration conditions. Bacterial removal efficiency in sand columns with the addition of biochar fabricated at 700 °C were higher than those fabricated at 400 °C and 550 °C due to its best bacterial adsorption capacity. Modification of biochar with arginine could further improve the bacterial removal performance. Specifically, complete bacterial removal (1.35 × 10⁷ ± 10% cells/mL) could be achieved under both slow and fast filtration conditions in sand columns with 1 wt% arginine functionalized biochar amendment. The enhanced bacterial adsorption capacity mainly contributed to the increased bacterial capture performance in columns with addition of arginine-modified biochar. Bacteria more tightly bounded with arginine-modified biochar than bulk biochar. Moreover, complete bacterial removal with the copresence of 5 mg/L humic acid in suspensions was acquired in columns with addition of 1 wt% arginine-modified biochar. Efficient bacterial removal in actual river water, multiple filtration cycles as well as longtime injection duration (100 pore volumes injection) was also obtained. The results of this study demonstrated that arginine-modified biochar had great potential to treat water contaminated by pathogenic bacteria.

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.

Kinetic study of nutrients removal from municipal wastewater by Chlorella vulgaris in photobioreactor supplied with CO2-enriched air

The microalgae Chlorella vulgaris ATCC 13482 was used in the present study for municipal wastewater treatment. Batch experiments were performed in bubble column photobioreactors of 7 L working volume maintained at 25 ± 2°C and 14 h/10 h of photo and dark cycle. The treatment process was enhanced by using CO₂-augmented air (5% CO₂ v/v) supply into the microalgal culture in comparison to the use of normal air (0.03% CO₂ v/v). For a period of 7 days, C. vulgaris effected maximum removals of 74.4% soluble fraction of chemical oxygen demand, 72% ammonia (NH₄-N), 60% nitrate (NO₃-N) and 81.93% orthophosphate (PO₄-P) with use of normal air, whereas 84.6% sCOD, 88% NH₄-N, 72% NO₃-N and 92.8% PO₄-P removals, respectively, with use of 5% CO₂/air supply. Using kinetic study data, the specific rates of ammonia and phosphate uptake (q_ammonia and q_phosphate) by C. vulgaris at 5% CO₂/air supply were found to be 2.41 and 0.85 d^-1, respectively. Using the algal remediation technology, nitrogen-phosphorus-potassium recovery from sewage treatment plant of 37.5 million litres per day wastewater influent capacity was calculated to be ∼298.5, 55.4 and 83.7 kg d^-1, respectively.

Phosphorus Removal and Carbon Dioxide Capture in a Pilot Conventional Septic System Upgraded with a Sidestream Steel Slag Filter

The objective of this work was to demonstrate the removal of the phosphorus and carbon dioxide capture potential of a conventional septic system upgraded with a sidestream steel slag filter used in recirculation mode. A pilot scale sidestream experiment was conducted with two septic tank and drainfield systems, one with and one without a sidestream slag filter. The experimental system was fed with real domestic wastewater. Recirculation ratios of 25%, 50% and 75% were tested. Limestone soils and non-calcareous soils were used as drainfield media. The tested system achieved a satisfactory compromise between phosphorus removal and pH at the effluent of the septic tank, thus eliminating the need for a neutralization step. The phosphorus removal efficiency observed in the second compartment of the septic tank was 30% in the slag filter upgraded system, compared to −3% in the control system. The slag filter reached a phosphorus retention of 105 mg/kg. The drainfield of non-calcareous soils achieved very high phosphorus removal in both control and upgraded systems. In the drainfield of limestone soil, the slag filtration reduced the groundwater phosphorus contamination load by up to 75%. The removal of chemical oxygen demand of the drainfields was not affected by the pH rise induced by the slag filter. Phosphorus removal in the septic tank with a slag filter was attributed to either sorption on newly precipitated calcium carbonate, or the precipitation of phosphate minerals, or both. Recirculation ratio design criteria were proposed based on simulations. Simulations showed that the steel slag filter partly inhibited the biological production of carbon dioxide in the septic tank. The influent alkalinity strongly influenced the recirculation ratio needed to raise the pH in the septic tank. The recirculation mode allowed clogging mitigation compared to a mainstream configuration, because an important part of chemical precipitation occurred in the septic tank. The control septic tank produced carbon dioxide, whereas the slag filter-upgraded septic tank was a carbon dioxide sink.

Leachability and plant-availability of phosphorus in post-sorption wastewater filters fortified with biochar

Sand and gravel are widely applied for filtering pre- or primary-treated wastewater in small-scale wastewater treatment (SWT) systems. However, ecological materials continue to attract increasing interest in use as retrofits for achieving better performance in removing dissolved contaminants and recovering nutrients from wastewater. In this study, we assessed the plant availability and leachability of phosphorus (P) from sand (Sa) and gas concrete (GC) media previously fortified with biochar (BC) and used for phosphorus (P) removal in laboratory-scale packed bed reactors and field-scale constructed filter beds. Batch and leaching experiments were conducted, with distilled water and ammonium lactate (AL) solutions (1:20 solid-liquid (w/v) ratio) applied as extractants. In the findings, reference (Sa) and fortified (Sa-BC) sand filters leached 11.2 and 20.5 mg P kg^-1 respectively, to percolating water while the P seemed less likely to leach from GC systems. Extraction with AL showed that P retained in GC was plant-available and that GC could release up to 90 mg kg^-1 of the bound mass. These findings highlight the need to evaluate risks of nutrient leaching from filter media for SWT systems especially where groundwater and surface water are final recipients of such effluents. For greater sustainability of use of the media, the weakly bound P in media such as Sa and BC and strongly bound in media such as GC types of materials may be recovered by recycling the spent material to agriculture. However, this may require re-design of the treatment system especially with respect to particle size to make recycling technically feasible.

Evaluation of five filter media in column experiment on the removal of selected organic micropollutants and phosphorus from household wastewater

A bench-scale column experiment was performed to study the removal of 31 selected organic micropollutants (MPs) and phosphorus by lignite, xyloid lignite (Xylit), granular activated carbon (GAC), Polonite^® and sand over a period of 12 weeks. In total 29 out of the 31 MPs showed removal efficiency >90% by GAC with an average removal of 97 ± 6%. Xylit and lignite were less efficient with an average removal of 80 ± 28% and 68 ± 29%, respectively. The removal efficiency was found to be impacted by the characterization of the sorbents and physicochemical properties of the compounds, as well as the interaction between the sorbents and compounds. For instance, Xylit and lignite performed well for relatively hydrophobic (log octanol/water partition coefficient (K_ow) ≥3) MPs, while the removal efficiency of moderately hydrophilic, highly hydrophilic and negatively charged MPs were lower. The organic sorbents were found to have more functional groups at their surfaces, which might explain the higher adsorption of MPs to these sorbents. The removal of several MPs improved after four weeks in sand, Xylit, GAC and lignite which may be related to increased biological activity and biofilm development. GAC and sand had limited ability to remove phosphorus (12 ± 27% and 14 ± 2%, respectively), while the calcium-silicate material Polonite^® precipitated phosphorus efficiently and increased the total phosphorus removal from 12% to 96% after the GAC filter.

Assessment of pollutant removal processes and kinetic modelling in vertical flow constructed wetlands at elevated pollutant loading

Constructed wetland (CW), an ecological wastewater treatment technology, is low cost and easily to operate. Vertical flow constructed wetland (VF-CW) systems have been used to treat various wastewaters across the world. The present work exhibits the detail study of five type's multi-layered vertically constructed wetlands operated at 24 h hydraulic retention time under semi-continuous vertical flow mode. Except N-NO₃^-, all the pollutants were sufficient removal in iron scraps constructed wetland (ISs-CW). The highest average pollutant removal efficiency achieved in ISs-CW was 85.04%, 77.57%, 85.99%, 62.01% and 88.91% for N-NH₄⁺, N-NO₂⁺, total nitrogen, total phosphate and sulphate respectively. The present CWs planted with Eichhornia crassipes is a promising system for municipal wastewater treatment. The first-order kinetic modelling was best suited for the removal rate since it presents higher R², rate constant (k) and B values.

Carbon-dioxide biofixation and phycoremediation of municipal wastewater using Chlorella vulgaris and Scenedesmus obliquus

The pure cultures of microalgae Chlorella vulgaris ATCC 13482 and Scenedesmus obliquus FACHB 417 were grown in municipal wastewater in 7-L airlift bubble column photobioreactor supplied with 5% CO₂/air (v/v). Batch experiments were conducted at 25 °C with 14-h light/10-h dark cycle for a period of 10 days. The CO₂ capture efficiencies for both the microalgae were monitored in terms of their respective biomass productivities, carbon contents, and CO₂ consumption rates. In the present study, the initial concentration of ammonia (43.7 mg L^-1) was decreased to 2.9 and 3.7 mg L^-1 by C. vulgaris and S. obliquus, respectively. And, the initial concentration of phosphate (18.5 mg L^-1) was decreased to 1.1 and 1.6 mg L^-1 by C. vulgaris and S. obliquus, respectively. CO₂ biofixation rates by C. vulgaris and S. obliquus, cultivated in municipal wastewater, were calculated to be 140.91 and 129.82 mg L^-1 day^-1, respectively. The findings from the present study highlight the use of microalgae for wastewater treatment along with CO₂ uptake and biomass utilization for pilot scale production of biodiesel, biogas, feed supplements for animals, etc., thus minimizing the production costs.

Dual slag filters for enhanced phosphorus removal from domestic waste water: performance and mechanisms

The phosphorus (P) removal of five combinations of dual filters consisting of blast furnace slag (BFS), argon oxygen decarburisation slag (AOD) and electric arc furnace slag (EAF) was evaluated in column experiments with domestic waste water. The columns were fed with waste water for 24 days. The column with only EAF had the best P removal performance (above 93% throughout the experiment). The speciation of the bound P was evaluated by P K-edge X-ray absorption near-edge structure (XANES) spectroscopy. In all five columns, the main P species of the slag packed in the outlet chamber was amorphous calcium phosphate (ACP). In samples from the inlet chambers, the contributions from crystalline Ca phosphates, P adsorbed on gibbsite and P adsorbed on ferrihydrite were usually much greater, suggesting a shift of P removal mechanism as the waste water travelled from the inlet to the outlet. The results provide strong evidence that P was predominantly removed by the slags through the formation of ACP. However, as the pH decreased with time due to the progressively lower dissolution of alkaline silicate minerals from the slag, the ACP was rendered unstable and hence redissolved, changing the P speciation. It is suggested that this process strongly affected the lifespan of the slag filters. Of the slags examined, EAF slag had the best P removal characteristics and BFS the worst, which probably reflected different dissolution rates of alkaline silicates in the slags.

Development and modelling of a steel slag filter effluent neutralization process with CO2-enriched air from an upstream bioprocess

The main objective of this project was to develop a steel slag filter effluent neutralization process by acidification with CO₂-enriched air coming from a bioprocess. Sub-objectives were to evaluate the neutralization capacity of different configurations of neutralization units in lab-scale conditions and to propose a design model of steel slag effluent neutralization. Two lab-scale column neutralization units fed with two different types of influent were operated at hydraulic retention time of 10 h. Tested variables were mode of flow (saturated or percolating), type of media (none, gravel, Bionest and AnoxKaldnes K3), type of air (ambient or CO₂-enriched) and airflow rate. One neutralization field test (saturated and no media, 2000-5000 ppm CO₂, sequential feeding, hydraulic retention time of 7.8 h) was conducted for 7 days. Lab-scale and field-scale tests resulted in effluent pH of 7.5-9.5 when the aeration rate was sufficiently high. A model was implemented in the PHREEQC software and was based on the carbonate system, CO₂ transfer and calcite precipitation; and was calibrated on ambient air lab tests. The model was validated with CO₂-enriched air lab and field tests, providing satisfactory validation results over a wide range of CO₂ concentrations. The flow mode had a major impact on CO₂ transfer and hydraulic efficiency, while the type of media had little influence. The flow mode also had a major impact on the calcite surface concentration in the reactor: it was constant in saturated mode and was increasing in percolating mode. Predictions could be made for different steel slag effluent pH and different operation conditions (hydraulic retention time, CO₂ concentration, media and mode of flow). The pH of the steel slag filter effluent and the CO₂ concentration of the enriched air were factors that influenced most the effluent pH of the neutralization process. An increased concentration in CO₂ in the enriched air reduced calcite precipitation and clogging risks. Stoichiometric calculations showed that a typical domestic septic tank effluent with 300 mg/L of biodegradable COD provides enough biological CO₂ for neutralization of a steel slag effluent with pH of 10.5-11.5. A saturated neutralization reactor with no media operated at hydraulic retention time of 10 h and a concentration of 2000 ppm in CO₂ enriched air is recommended for full-scale applications.

Impact of on-site, small and large scale wastewater treatment facilities on levels and fate of pharmaceuticals, personal care products, artificial sweeteners, pesticides, and perfluoroalkyl substances in recipient waters

One of the main risks associated with effluents from both wastewater treatment plants (WWTPs) and on-site sewage treatment facilities (OSSFs) is the release of micropollutants (MPs) in receiving water bodies. However, the impact of MPs present in the effluents of OSSFs in the aquatic environment has not been studied so far. The current study evaluates the impact of the effluents of OSSFs and small-to-large scale WWTPs on natural waters. The discharge of 74 MPs was assessed including pharmaceuticals, personal care products, pesticides, artificial sweeteners and perfluoroalkyl substances (PFASs). The sampling was carried out within a Swedish catchment and included three sites that are exclusively affected by OSSFs and other sites that are mainly affected by WWTPs or a mixture of sources (7 sites, 28 samples). Results show that although OSSFs serve a much smaller total number of people, the MPs emitted from OSSFs reached the aquatic environment in significant quantities (concentrations of >150ngL^-1 of ∑MPs). The composition profiles for sites affected by WWTPs were similar and were dominated by sucralose (27% of the ∑MPs), caffeine (27% of the ∑MPs), lamotrigine (10% of the ∑MPs), desvenlafaxine (5% of the ∑MPs), and diclofenac (4% of the ∑MPs). In contrast, the sites affected by OSSFs showed high variability, exhibiting a different profile from those affected by WWTPs and also from each other, demonstrating that OSSFs are not homogeneous sources of MPs. Some specific compounds, such as diethyltoluamide (DEET) and caffeine, were proportionally much more important at sites affected by OSSFs than at sites affected by WWTPs (representing a much higher percentage of the ∑MPs in the OSSFs). In contrast, PFASs did not show high concentration variation among the different sampling sites and the composition profiles were relatively similar, indicating that these substances follow different routes of entry into the aquatic environment.

Evaluation of thermally-modified calcium-rich attapulgite as a low-cost substrate for rapid phosphorus removal in constructed wetlands

The cost-effective and geographically available substrates are vital for the design of constructed wetlands (CWs), especially the saturated subsurface flow CWs, which are deemed as an efficient way to remove the inlet-lake phosphorus concentrations. In this study, phosphorus removal of thermally-treated calcium-rich attapulgite (TCAP) with varied particle sizes (0.2-0.5 mm, 0.5-1 mm and 1-2 mm) was assessed using batch and long-term column experiments to evaluate its feasibility as a CWs substrate. The phosphorus-bound mechanism in TCAP was identified in various initial phosphorus concentrations. Batch studies indicated that more than 95% of P can be rapidly (<1 h) removed by TCAP from solution with a concentration of 20 mg P/L, and P sorption can be well fitted by a pseudo-second-order equation. The maximum P sorption capacity of TCAP was in the range of 4.46-5.99 mg P/g, and the availability of Ca²⁺ concentration might limit the P removal capacity of TCAP at high phosphorus concentrations. Both the P removal rate and capacities decreased with the increase of TCAP particle sizes. Column P removal experiments indicated that hydraulic retention time (HRT) exerts great influence on P removal performance and longer HRTs favor the dissolution of CaO in TCAP, consequently increasing the P removal rate. In a 150-day P removal experiment, TCAP removed an average of 93.1%-95.4% of the influent P with a HRT of eight hours. Both the batch and chemical extraction of the P fraction of TCAP showed that the P removed by TCAP was mainly through formation of Ca phosphate precipitation. However, the species of Ca-P precipitation formed might be varied in different phosphorus concentrations. All results indicated that TCAP can be a suitable substrate when used in CWs, and field experiments should be carried out to test its real P removal performance in the future.

Screening and prioritization of micropollutants in wastewaters from on-site sewage treatment facilities

A comprehensive screening of micropollutants was performed in wastewaters from on-site sewage treatment facilities (OSSFs) and urban wastewater treatment plants (WWTPs) in Sweden. A suspect screening approach, using high resolution mass spectrometry, was developed and used in combination with target analysis. With this strategy, a total number of 79 micropollutants were successfully identified, which belong to the groups of per- and polyfluoroalkyl substances (PFASs), pesticides, phosphorus-containing flame retardants (PFRs) and pharmaceuticals and personal care products (PPCPs). Results from this screening indicate that concentrations of micropollutants are similar in influents and effluents of OSSFs and WWTPs, respectively. Removal efficiencies of micropollutants were assessed in the OSSFs and compared with those observed in WWTPs. In general, removal of PFASs and PFRs was higher in package treatment OSSFs, which are based on biological treatments, while removal of PPCPs was more efficient in soil bed OSSFs. A novel comprehensive prioritization strategy was then developed to identify OSSF specific chemicals of environmental relevance. The strategy was based on the compound concentrations in the wastewater, removal efficiency, frequency of detection in OSSFs and on in silico based data for toxicity, persistency and bioaccumulation potential.

Phosphorus removal from wastewater by field-scale fortified filter beds during a one-year study

Due to low availability of alternative technologies, rural communities are unable to comply with national wastewater discharge limits. This study tested the effectiveness of filter bed fortification with biochar on phosphorus removal. Water-tight down-flow beds of sand and gas concrete, constructed alongside a reference sand bed (all 0.8 m deep and 0.75 m(2) surface area), were topped with a 0.2 m biochar layer. Pre-treated domestic wastewater with mean concentrations of 6.4 mg/L [Formula: see text] and 142.6 NTU, was infiltrated at 4 cm/d hydraulic loading rate. Ultimately, the biochar-sand was relatively outstanding in turbidity reduction, achieving <5 NTU. The biochar-gas concrete exhibited superior performance in [Formula: see text] removal, trapping 32.3 g (40.2%), compared with 20.5 g (25.6%) and 15.5 g (19.3%) by biochar-sand and reference bed respectively. However, statistical analysis revealed a weak correlation between pH and biochar-gas concrete removal efficiency (r(2 )= 0.2). The relationship was stronger for biochar-sand [Formula: see text] (r(2 )= 0.5) than reference (r(2 )= 0.4) bed. Paired samples t-tests showed that incorporating biochar into the sand bed significantly (p = .04) improved its [Formula: see text] removal efficiency. In conclusion, sand bed fortification with biochar could be an important measure for improving P removal and wastewater clarification efficiency.

Sequential UASB and dual media packed-bed reactors for domestic wastewater treatment - experiment and simulation

A wastewater treatment system composed of an upflow anaerobic sludge blanket (UASB) reactor followed by a packed-bed reactor (PBR) filled with Sorbulite(®) and Polonite(®) filter material was tested in a laboratory bench-scale experiment. The system was operated for 50 weeks and achieved very efficient total phosphorus (P) removal (99%), 7-day biochemical oxygen demand removal (99%) and pathogenic bacteria reduction (99%). However, total nitrogen was only moderately reduced in the system (40%). A model focusing on simulation of organic material, solids and size of granules was then implemented and validated for the UASB reactor. Good agreement between the simulated and measured results demonstrated the capacity of the model to predict the behaviour of solids and chemical oxygen demand, which is critical for successful P removal and recovery in the PBR.

Phosphorus removal performance and speciation in virgin and modified argon oxygen decarburisation slag designed for wastewater treatment

Argon oxygen decarburisation (AOD) slag may be used for phosphorus (P) removal, as its high pH and weatherable calcium (Ca) minerals provide sufficient Ca(2+) and OH(-) for calcium phosphate (Ca-PO4) precipitation. This study examined the P removal performance of AOD slag for use as wastewater treatment material. Batch experiments were carried out using both synthetic P solution and real wastewater, followed by chemical modelling and X-ray absorption near edge structure (XANES) spectroscopy. The influences of initial P concentration, slag dose and modification by polyethylene glycol (PEG), an effective agent for generation of porous materials, were investigated to determine the optimal conditions for P removal by AOD slag. It was found that virgin AOD slag removed 94.8% of P from a synthetic P solution in 4 h and 97.8% in 10 h. This high P removal was accompanied by a rapid increase in pH from 7.0 to 10.74. The maximum P removal capacity (PRC) from synthetic P solution ranged from 1.3 to 27.5 mg P g(-1). The optimal AOD dose for P removal from wastewater, determined in 8-h batch experiments, was 25 g L(-1). PEG modification increased the reaction rate and resulted in higher final pH, increasing PRC by 47.9%. Combined Visual MINTEQ and XANES analysis for detailed examination of P removal mechanisms revealed that the main P removal mechanism was precipitation of calcium phosphate. According to the XANES analysis, the main Ca-PO4 precipitate formed on virgin AOD slag under low initial P concentration and high pH was apatite, while brushite was the dominant product at high initial P concentration and low pH.