Removal of ammoniacal-nitrogen from an artificial landfill leachate in downflow reed beds

Aging behavior and leaching characteristics of microfibers in landfill leachate: Important role of surface mesh structure

Mesh-structured films formed by the post-processing of microfibers improves their permeability and dexterity, such as disposable masks. However, the aging behavior and potential risks of mesh-structured microfibers (MS-MFs) in landfill leachate remain poorly understood. Herein, the aging behavior and mechanisms of MS-MFs and ordinary polypropylene-films (PP-films) microplastics, as well as their leaching concerning dissolved organic matter (DOM) in landfill leachate were investigated. Results revealed that MS-MFs underwent more significant physicochemical changes than PP-films during the aging process in landfill leachate, due to their rich porous habitats. An important factor in the photoaging of MS-MFs was related to reactive oxygen species produced by DOM, and this process was promoted by photoelectrons under UV irradiation. Compared with PP-films, MS-MFs released more DOM and nano-plastics fragments into landfill leachate, altering the composition and molecular weight of DOM. Aged MS-MFs-DOM generated new components, and humus-like substances produced by photochemistry showed the largest increase. Correlation analysis revealed that leached DOM was positively correlated with oxygen-containing groups accumulated in aged MS-MFs. Overall, MS-MFs will bring higher environmental risks and become a new long-term source of DOM contaminants in landfill leachate. This study provides new insights into the impact of novel microfibers on landfill leachate carbon dynamics.

Preparation of artificial MSW leachate for treatment studies: Testing on black soldier fly larvae process

When approaching the study of new processes for leachate treatment, each influencing variable should be kept under control to better comprehend the treatment process. However, leachate quality is difficult to control as it varies dramatically from one landfill to another, and in line with landfill ageing. To overcome this problem, the present study investigated the option of preparing a reliable artificial leachate in terms of quality consistency and representativeness in simulating the composition of real municipal solid waste (MSW) leachate, in view of further investigate the recent treatment process using black soldier fly (BSF) larvae. Two recipes were used to simulate a real leachate (RL): one including chemical ingredients alone (artificial synthetic leachate-SL), and the other including chemicals mixed with artificial food waste (FW) eluate (artificial mixed leachate-ML). Research data were analysed, elaborated and discussed to assess simulation performance according to a series of parameters, such as Analytical representativeness, Treatment representativeness (in this case specific for the BSF larvae process), Recipe relevance, Repeatability and Flexibility in selectively modifying individual quality parameters. The best leachate simulation performance was achieved by the synthetic leachate, with concentration values generally ranging between 97% and 118% of the RL values. When feeding larvae with both RL and SL, similar mortality values and growth performance were observed.

The Imperative Need of Metal Salt for the Treatment of Industrial Wastewater via the Synergic Coagulation-Flocculation Method

Tile industry wastewater is known to contain a high concentration of TSS and turbidity resulting from various raw materials. In the present study, the effectiveness of the coagulation process on turbidity and TSS removal from Kuwait ceramic tile industry wastewater was investigated using ferric chloride as a coagulant. The experiments were conducted using jar tests to determine the optimum operating conditions of coagulant dosages, pH, and settling time. It was found that the coagulant dosage and medium pH greatly affect the efficiency of the coagulation process. A gradual increase in coagulant dosage from 10 to 50 mg/L increased the efficiency of turbidity removal from 95.6% to 99.5%. The efficiency of the coagulation process was also found to be dependent on pH values, where higher pH improved the efficiency of turbidity removal. It was found that a medium pH of 10, 1 h settling time, and 50 mg/L of coagulant dosage are the optimum process conditions to achieve almost complete removal of turbidity (99.5%) and TSS (99.8%). This study concluded that coagulation might be useful as a primary wastewater treatment process for tile industry wastewater.

Pollutant removal from landfill leachate employing two-stage constructed wetland mesocosms: co-treatment with municipal sewage

Constructed wetlands are low-cost, natural technologies that are often employed for the treatment of different types of wastewater. In this study, landfill leachate and municipal wastewater were co-treated by the three parallel two-stage Phragmites- or Vetiver-based constructed wetland mesocosms. Two-stage wetland mesocosms included vertical flow (VF) units as the first stage, followed by horizontal flow (HF)/surface flow (SF)/floating treatment (FT) units. VF and HF wetland mesocosms were filled with gravel, steel slag, concrete block, and intermittent carbon-saturated ceramic filters as substrates. Mean input nitrogen, organics, and phosphorus load across first stages were 75 g N/m² day, 283 g COD/m² day, 88 g BOD/m² day, and 10 g P/m² day, respectively. N and P accumulation rate was not substantial (< 10%) with respect to total removal in most wetland mesocosms. Gravel-based VF wetland mesocosm achieved better NH₄-N and BOD removal (55-59%) during landfill leachate treatment phase, when compared with co-treatment periods (12-52%). Slag-concrete- and ceramic filter-based VF wetland mesocosms maintained stable NH₄-N and BOD removals; the former wetland mesocosm was the most efficient VF unit (than other two wetland mesocosms) due to media characteristics. Media-based adsorption accelerated P removal (93%) in slag-concrete-based VF wetland mesocosm. Carbon scarcity limited denitrification in all VF wetland mesocosms; removal of TN was < 32%. Second stage wetland mesocosms achieved higher nitrogen (85-92%), organics (66-90%), and phosphorus (97-100%) removals regardless of operational variations; low input load, long retention time, media, and rhizosphere enhanced removal performances, particularly in HF and FT wetland mesocosms. In general, this study demonstrates potential application of two-stage wetland mesocosms for landfill leachate treatment or co-treatment with municipal sewage.

Vertical flow wetlands and hybrid systems for the treatment of landfill leachate

Landfill leachates contain a variety of toxic compounds, which makes them one of the most difficult types of wastewater to be treated. An alternative "green" technology for leachate treatment is the use of constructed wetlands (CWs). The aims of this study were to select macrophytes and substrates to be used in vertical flow wetlands (VFWs) and to evaluate the performance of hybrid systems composed by a VFW and a horizontal subsurface flow (HSSW) or a free water surface flow (FWSW) wetlands for the treatment of a high ammonium concentration landfill leachate. In microcosms scale experiments, Typha domingensis, Scirpus californicus, and Iris pseudacorus were studied to assess their tolerance to raw and diluted leachate. Substrate selection for VFWs was evaluated using different layers of light expanded clay aggregate (LECA), coarse sand, fine sand, and gravel. Contaminant removals were higher in planted than in unplanted wetlands. Plants did not tolerate the raw effluent but showed a positive effect on plant growth when exposed to the diluted leachate. T. domingensis and I. pseudacorus showed higher contaminant removal ability and tolerance to landfill leachate than S. californicus. VFW with LECA + coarse sand showed the best performance in removal efficiencies. Hybrid system composed by VFW-FWSW planted with T. domingensis presented the best performance for the treatment of landfill leachate with high concentrations of ammonium.

Nitrogen removal efficiencies and pathways from unsaturated and saturated zones in a laboratory-scale vertical flow constructed wetland

A laboratory-scale vertical flow constructed wetland system was designed and monitored to compare nitrogen removal rates and pathways from both saturated and unsaturated zones under a hydraulic loading rate and influent total nitrogen concentration of 1.5 m³/m².d and 508 mg/L respectively. Weekly measurements of the concentrations of nitrogen compounds, chemical oxygen demand, temperature, dissolved oxygen, oxidation-reduction potential, and hydrogen ion concentration were taken throughout the study. At the end of the experiments, PCR analysis of 16S rRNA gene sequencing was performed to identify microbial communities in the unsaturated and saturated parts of the system. The nitrogen compounds were removed from the system after 182 days, with similar total nitrogen removal efficiencies (94% and 93%) for the unsaturated and saturated zones respectively. Heterotrophic nitrification/aerobic denitrification was the major pathway responsible for the removal of nitrogen compounds. Adsorption into the gravel bed also contributed to ammonium removal. Proteobacteria were the dominant bacterial strains involved in nitrogen transformation and accounted for 80% of the total bacteria in the unsaturated zone and 60% in the saturated zone. With little difference in the concentration removal efficiencies of the unsaturated and saturated zones, a more effective design would be an entirely saturated wetland as the total mass removal of nitrogen depends on the water volume stored, which at full saturation in this design was seven times greater per unit wetland volume than the unsaturated zone.

Removal of heavy metals from synthetic landfill leachate in lab-scale vertical flow constructed wetlands

Synthetic landfill leachate was treated using lab-scale vertical flow constructed wetlands (CWs) in sequencing batch modes to assess heavy metal removal efficiencies. The CWs filled with loamy soil and pumice stone were unplanted or planted with common reed (Phragmites australis) (Reed-CW) or common rush (Juncus effusus) (Rush-CW). Synthetic leachate contained acetate, propionate, humate, ammonium, and heavy metals. Common reed grew almost vigorously but common rush partly withered during the 8-month experiment. The CWs reduced the leachate volume effectively by evapotranspiration and removed easily degradable organic matter, color, and ammonium. Furthermore, the CWs demonstrated high removal amounts for heavy metals such as Zn, Cr, Ni, Cd, Fe, and Pb, but not Mn from leachate. The metal removal amounts in the CWs were low for high-strength leachate (influent concentration increased from one time to three times) or under short retention time (batch cycle shortened from 3days to 1day). The Rush-CW showed slightly lower removal amounts for Cr, Ni, Mn, and Cd, although the Reed-CW showed lower Mn removal amounts than the unplanted CW did. However, Cd, Cr, Pb, Ni, and Zn were highly accumulated in the upper soil layer in the planted CW by rhizofiltration with adsorption compared with unplanted CW, indicating that the emergent plants would be helpful for decreasing the dredging soil depth for the final removal of heavy metals. Although the emergent plants were minor sinks in comparison with soil, common rush had higher bioconcentration factors and translocation factors for heavy metals than common reed had.

Stormwater nutrient attenuation in a constructed wetland with alternating surface and subsurface flow pathways: Event to annual dynamics

Among different Water Sensitive Urban Design (WSUD) options, constructed wetlands (CWs) are widely used to protect and support downstream urban waterways from stormwater nutrients. This analysis assessed the nutrient attenuation ability of a novel CW in Western Australia that combined multiple alternating surface flow (SF) and laterite-based subsurface flow (SSF) compartments within a parkland context to improve the urban landscape and amenity. The CW was designed to maximise nutrient reduction despite experiencing a large range of hydrologic conditions, from low transit time nutrient-rich pulses during the wet periods to prolonged low to zero flow conditions during the dry periods. The CW design was further complicated by the possibility of ungauged water inputs after wet antecedent conditions, seasonal macrophyte senescence and a recirculation system to maintain flow during the dry periods. From analysis of data over a range of time scales, we determined that overall the CW attenuated up to 62% total nitrogen (TN) and 99% total phosphorus (TP) loads during dry weather conditions, and 54-76% TN and 27-68% TP during episodic flow pulses. N species attenuation was dominant in the SF compartments, while P species were attenuated mostly within the SSF compartments. Nutrient accumulation in the sediments, and above and below ground biomass of the macrophytes were found to increase during the early stages of operation, suggesting the system reached equilibrium within four years. Further, by comparing trends in nutrient attenuation within the context of diel changes in high frequency oxygen data from different compartments, it was demonstrated that changes in dissolved oxygen were related to changes in nutrient concentration across the CW, although interpretation of this was complicated by changing hydro-climatological conditions. The implementation of this CW concept in a highly seasonal Mediterranean climate demonstrates that urban liveability and environmental health can both be improved through careful design.

A review on nitrogen and organics removal mechanisms in subsurface flow constructed wetlands: dependency on environmental parameters, operating conditions and supporting media

With the unique advantages of lower operational and maintenance cost, the applications of subsurface flow constructed wetlands for the treatment of wastewater have been increasing rapidly throughout the world. The removal of nitrogen and organics by such systems has gained substantial attention in recent years. In subsurface flow wetlands, the removal of pollutants often relies on a diverse range of co-existing physical, chemical and biological routes, which are vitally dependent on numerous environmental and operational parameters. This paper provides a comprehensive review of wetland structures, classic and novel nitrogen and organics removal mechanisms along with the key environmental parameters and operational conditions that enhance removal in subsurface flow wetland systems. The critical exploration identifies the major environmental parameters such as: pH, DO, and temperature, operational factors i.e. organic carbon availability, loading, feed mode, retention time, recirculation, harvesting, and the complex role (of both parameters) on classical nitrogen and organics removal pathways. Subsequently, the necessity of further extensive research on such factors, for promoting novel nitrogen removal routes in wetland systems has also been highlighted. The expansion of the review on the influence of the unconventional wetland matrix indicates that, the structural differences and inherent properties of these media can support substantial nitrogen and organics removal from wastewater, under optimal operating conditions. Overall, the critical review illustrates the necessity of a profound knowledge on the complicated inter-relationship between nitrogen and organics removal routes, governing environmental and operational parameters, and wetland matrix for improving the treatment performances of subsurface flow wetlands.

Treatment of landfill leachate with high levels of ammonia by constructed wetland systems

Landfill leachate treatment can be expensive and energy-intensive when achieved in advanced wastewater treatment plants. One possible method to reduce cost and energy requirements is to treat the leachate on-site using constructed wetlands. In this study, we investigated the feasibility of treating the leachate from a 10-year-old landfill site, with high levels of ammonia, by lab-scale constructed wetland microcosms. Five different types of wetland systems were used in the test: P1, P2 and CS-1 systems fed by original leachate, P3 and CS-2 systems fed by secondarily treated leachate. The CS systems were used as control without vegetation. Each system contained two basins connected in series: one installed as free water surface (FWS) wetland microcosm, and the other as subsurface flow (SSF) wetland microcosm. After one year of operation, the experimental results showed that P2 system performed better than both P1 and P3 systems by comparing their removal efficiencies of ammonia, which were measured equal to 94%, 84% and 60%, respectively. However, for total nitrogen removal, all three systems exhibited lower values, which meant that the process denitrification was insignificant in the wetland systems treating aged leachate. According to the experimental results of adding extra BOD into the systems, we found that the reason was due to lack of organic carbon sources in aged leachate for denitrification, which might cause nitrate buildup in the effluents.

Anaerobic membrane bioreactor for the treatment of leachates from Jebel Chakir discharge in Tunisia

Landfill leachate (LFL) collected from the controlled discharge of Jebel Chakir in Tunisia was treated without any physical or chemical pretreatment in an anaerobic membrane bioreactor (AnMBR). The organic loading rate (OLR) in the AnMBR was gradually increased from 1 g COD l(-1)d(-1) to an average of 6.27 g COD l(-1)d(-1). At the highest OLR, the biogas production was more than 3 volumes of biogas per volume of the bioreactor. The volatile suspended solids (VSSs) reached a value of approximately 3 g l(-1) in the bioreactor. At stable conditions, the treatment efficiency was high with an average COD reduction of 90% and biogas yield of 0.46 l biogas per g COD removed.

Influence of recirculation in a lab-scale vertical flow constructed wetland on the treatment efficiency of landfill leachate

Landfill leachate taken from a landfill situated in the north-western region of Bulgaria has been treated in a laboratory scale vertical flow constructed wetland (VF-CW) at different flow rates (40, 60 and 82 ml min(-1)) and recirculation ratios (time of water running through wetland to time of quiet water - 1:1; 1:2; 1:3). Young Phragmites australis was planted on the top layer of the reactor. The low flow rate (40 ml min(-1)) and recirculation ratio of 1:3 allowed removal efficiencies of 96% for COD (in 8 days), 92% for BOD(5) (in 3 days), 100% for ammonia (in 5 days) and 100% for total phosphorus (in 2 days). At the highest flow rate studied (82 ml min(-1)) and shorter quiet period (recirculation ratio 1:1) the water needs longer period of treatment (2 days more according to COD). The results of this study indicate that both flow rate and recirculation ratio should be taken into account for proper design of VF-CW.

Application of response surface methodology (RSM) to optimize coagulation-flocculation treatment of leachate using poly-aluminum chloride (PAC) and alum

Coagulation-flocculation is a relatively simple physical-chemical technique in treatment of old and stabilized leachate which has been practiced using a variety of conventional coagulants. Polymeric forms of metal coagulants which are increasingly applied in water treatment are not well documented in leachate treatment. In this research, capability of poly-aluminum chloride (PAC) in the treatment of stabilized leachate from Pulau Burung Landfill Site (PBLS), Penang, Malaysia was studied. The removal efficiencies for chemical oxygen demand (COD), turbidity, color and total suspended solid (TSS) obtained using PAC were compared with those obtained using alum as a conventional coagulant. Central composite design (CCD) and response surface method (RSM) were applied to optimize the operating variables viz. coagulant dosage and pH. Quadratic models developed for the four responses (COD, turbidity, color and TSS) studied indicated the optimum conditions to be PAC dosage of 2g/L at pH 7.5 and alum dosage of 9.5 g/L at pH 7. The experimental data and model predictions agreed well. COD, turbidity, color and TSS removal efficiencies of 43.1, 94.0, 90.7, and 92.2% for PAC, and 62.8, 88.4, 86.4, and 90.1% for alum were demonstrated.

Completely autotrophic nitrogen-removal over nitrite in lab-scale constructed wetlands: evidence from a mass balance study

A mass-balance study was carried out to investigate the transformation of nitrogenous pollutants in vertical flow wetlands. Landfill leachate containing low BOD, but a high concentration of ammonia, was treated in four wetland columns under predominately aerobic conditions. Influent total nitrogen in the leachate consisted mainly of ammonia with less than 1% nitrate and nitrite, and negligible organic nitrogen. There was a substantial loss of total nitrogen (52%) in one column, whereas other columns exhibited zero to minor losses (<12%). Net nitrogen loss under study conditions was unexpected. Correlations between pH, nitrite and nitrate concentrations indicated the removal of nitrogen under study conditions did not follow the conventional, simplistic, chemistry of autotrophic nitrification. Through mass-balance analysis, it was found that CANON (Completely Autotrophic Nitrogen-removal Over Nitrite) was responsible for the transformation of nitrogen into gaseous form, thereby causing the loss of nitrogen mass. The results show that CANON can be native to aerobic engineered wetland systems treating wastewater that contains high ammonia and low BOD.