High Hydraulic Loading Rate Research Articles

Design of a zero liquid discharge leachate treatment system using an evapotranspiration willow bed

While zero liquid discharge (ZLD) wetlands have been successfully used for domestic wastewater treatment, adapting this technology to treat other wastewaters such as leachate could be very attractive for some industries concerned with meeting increasingly stringent environmental regulations. Leachate treatment typically implies large volume of water that are entirely dependent on rainfall and therefore highly variable both throughout the year and between years. Current design guidelines for zero discharge willow systems limit system flexibility because they are based on rough theoretical estimates of evapotranspiration. This discuss the applicability of ZLD treatment through a willow bed evapotranspiration (ET) applied to the treatment of industrial leachate that has high and variable hydraulic loading rate and low contaminant and salt concentration. We propose a base design and, through detailed and long-term hydrological modeling of such a treatment system, investigate how various design and management decisions can affect sizing, efficiency, and overall feasibility of the technology. We showed that considering ET optimization factors (e.g. fertilization and organic substrate) was essential for ZLD to be achieved over a 20-year period in northern continental humid climate and that the ratio between cumulative annual ET of the willow bed and cumulative annual rainfall should be at least 1.5. When varying the leachate collection area, it was found that a ratio of willow bed area to collection area between 0.5 and 0.7 should be expected for an optimized design in this specific climate, were land area and storage volume remain the most limiting factors. Regarding storage volume, several management options can be applied to reduce the volume of storage required. We also highlight that a risk attenuation strategy should always be included in the design of a ZLD wetland system. Our study suggests that ZLD wetlands constitute a green technology that represents a serious alternative treatment method for pretreated leachate, while offering many benefits such as low maintenance and energy costs, valorization of contaminants such as nitrogen or phosphorus through biomass production, and, most importantly, zero contaminant discharge to the environment. Finally, we propose future research opportunities and other possible applications for further development of the technology.

Evaluation of the removal performance in long-term operation of bioaugmented subsurface wastewater infiltration systems under a high hydraulic loading rate

To enhance the pollutant removal performance of a subsurface wastewater infiltration system (SWIS) used in decentralized treatment of domestic sewage, two nitrogen-removing strains were isolated from a SWIS with high removal efficiency and inoculated into another SWIS. Three SWISs were analyzed: a sterilized SWIS (system 1), a control SWIS (system 2), and a bioaugmented SWIS (system 3). Under the conditions of 0.28 m3/m2 ⋅ d hydraulic loading rate and 716 d running time, the removal capacities of COD, NH4+-N, TN and TP of system 3 were 167.19 ± 14.21 mg/L ⋅ d, 23.85 ± 0.74 mg/L ⋅ d, 25.21 ± 0.96 mg/L ⋅ d and 6.46 ± 0.06 mg/L ⋅ d, respectively. Correspondingly, the removal efficiencies of COD, NH4+-N and TN were 89.63%, 92.69%, and 86.95%, respectively, which were 6.41%, 6.45%, and 11.48% higher than those of system 2 and 63.01%, 55.15%, and 51.27% higher than those of system 1. The concentrations of COD, NH4+-N, TN and TP of system 3 stabilized at depths of 130 cm, 110 cm, 150 cm, and 130 cm, respectively. Additionally, both the number of nitrifying/denitrifying bacteria and the nitrate/nitrite reductase activity (NRA/NIRA) showed that the nitrogen removal zone was 90–130 cm deep. The coefficients of determination (R2) between NO3−-N concentrations and the number of denitrifying bacteria/NR activities in system 3 showed the greatest correlation, which were 0.97 at 150 cm and 0.92 at 90 cm. Bioaugmentation by the re-inoculation of strains isolated from a SWIS into new SWIS could be an ideal method to improve the performance and service life of SWISs.

Estimating the Importance of Hydrologic Conditions on Nutrient Retention and Plant Richness in a Wetlaculture Mesocosm Experiment in a Former Lake Erie Basin Swamp

The western basin of Lake Erie, the shallowest of the Laurentian Great Lakes in North America, is now plagued by harmful algal blooms annually due to nutrient discharges primarily from its basin. Water quality was impacted so significantly by toxic cyanobacteria in 2014 that the city of Toledo’s water supply was shut off, affecting hundreds of thousands of residents. A new agricultural land management approach, ‘wetlaculture (=wetland + agriculture)’, has a goal of reducing the need for fertilizer applications while preventing fluxes of nutrients to downstream aquatic ecosystems. A wetlaculture mesocosm experiment was set up on agricultural land near Defiance, Ohio, on the northwestern edge of the former ‘Great Black Swamp’. The mesocosms were randomly assigned to four hydrologic treatments involving two water depths (no standing water and ~10-cm of standing water) and two hydraulic loading rates (10 and 30 cm week−1). Nearby agricultural ditch water was pumped to provide weekly hydraulic loading rates to the mesocosms. During the two-year period, the net mass retention of phosphorus from the water was estimated to have averaged 1.0 g P m−2 in the wetland mesocosms with a higher hydraulic loading rate, while the highest estimated net nitrogen mass retention (average 22 g N m−2) was shown in the wetland mesocosms with 10 cm of standing water and higher hydraulic loading rate. Our finding suggests that hydrologic conditions, especially water level, contribute directly and indirectly to nutrient retention, partially through the quick response of the wetland vegetation community. This study provides valuable information for scaling up to restore significant areas of wetlaculture/wetlands in the former Great Black Swamp, strategically focused on reducing the nutrient loading to western Lake Erie from the Maumee River Basin.

Evaluation of the influence of filter medium composition on treatment performances in an open-air green wall fed with greywater

According to the European Research and Innovation Policy Agenda, nature-based solutions (NBSs) are key technologies to improve the sustainability of urban areas. Among NBSs, green walls have been recently studied for several applications, among the others the treatment of lowly polluted wastewater flows as greywater (GW, e.g. domestic wastewater excluding toilet flushes). This work is aimed at the evaluation of the influence of four additives (compost, biochar, granular activated carbon, polyacrylate) mixed with a base filter medium made of coconut fibre and perlite, on the performances of a green wall fed in batch mode with synthetic GW. The green wall was operated with a high hydraulic loading rate of GW (740.8 L/m2/day) in open-air winter conditions (3.5–15 °C measured for GW) between January and April. The performances of the green wall have been assessed though the monitoring every 1–2 weeks of physicochemical and biological parameters (pH, electric conductivity, total suspended solids, dissolved oxygen, BOD5 and COD, nitrogen and phosporus compounds, chlorides and sulphates, anionic surfactants and E. coli). Removal performances were excellent for BOD5 (>95%) and E.coli (>98%) for all additives; compared to the base medium, biochar was the best performing additive over the highest number of parameters, achieving removals equal to 51% for COD, 47% for TKN and nitric nitrogen and 71% for anionic surfactants. Compost also achieved high removal performances, but the frequent clogging events occurred during the monitoring period do not make its use recommendable. Granular activated carbon and the combination of biochar and polyacrylate performed better than the base medium, but only about the removal of nitric nitrogen. These results demonstrated that, in the considered experimental boundaries, biochar could improve the overall treatment performances of a green wall fed by GW and operated in challenging conditions.

Per‐ and polyfluoroalkyl substances removal with granular activated carbon and a specialty adsorbent: A case study

AbstractRemoval of per‐ and polyfluoroalkyl substances (PFAS) from water sources is of significant interest as many states have established limits. Three granular activated carbons (GACs) and a clay‐based adsorbent, Fluoro‐sorb® 200 (FS200), were tested using rapid small scale column tests (RSSCTs) to compare relative performance of the media for PFAS removal. FS200 effluent was below detection for all PFAS except PFHxA at 300,000 bed volumes (BVs). The three GACs performed similarly except for PFBS and PFHxA. FS200 showed higher BVs to breakthrough, required a significantly shorter empty bed contact time, and had higher hydraulic loading rate, translating into a smaller footprint than GAC. This work provides important contributions to the water treatment literature, including RSSCT evaluation of FS200 media and media life comparison of GAC and FS200 in drinking water matrices with low PFAS and organic carbon concentrations.Article Impact StatementUtilities needing PFAS treatment will benefit from the testing methodology and results.

Decentralized Domestic Sewage Treatment Using an Integrated Multi-Soil-Layering and Subsurface Wastewater Infiltration System

In this study, an integrated multi-soil-layering and subsurface wastewater infiltration (MSL-SWI) system was developed for decentralized domestic sewage treatment under high hydraulic loading rates (HLRs). To improve sustainable nitrogen removal, the influence of intermittent operation and shunt distributing wastewater on the performance of MSL-SWI systems was investigated. The optimal performance—with removal efficiencies of 93.41% for chemical oxygen demand, 97.91% for total phosphorus, 74.02% for ammonia nitrogen, and 73.56% for total nitrogen—was achieved using both intermittent operation and shunt distributing wastewater under an HLR of 0.3 m3 m−2 d−1. The activity of microbial nitrogen functional genes (i.e., amoA, nirK, nirS, nosZ, and anammox 16S rRNA) and their relationships with nitrogen transformation rates were further analyzed in different layers of the system. The results imply that nitrification and anaerobic ammonium oxidation in the MSL section coupled with nitrification and denitrification in the SWI section contribute to main the mechanisms of sustainable nitrogen removal. In summary, MSL-SWI systems not only operate with high efficiency under high HLRs, but the contaminant removal is also stable and sustainable, which are promising properties for domestic sewage treatment in areas where land resources are limited.

Performance and Energy Consumption Evaluation of Rotating Biological Contactor for Domestic Wastewater Treatment

Biological processes are extensively used for wastewater treatment because of low organic footprint, economically feasible, and high treatment efficiency. Rotating biological contactors (RBC), an attached growth biological process offers advantage of low operating cost, simple configuration and structure, reduced bionomical footprint and thus has been extensively employed for organics and nitrogen removal. In this study, RBC was used for the treatment of synthetic domestic wastewater operating at high hydraulic and organic loading rate to demonstrate the biological performance. The results showed that the RBC achieved a treatment efficiency for COD, ammonium, TN and turbidity of 70.2%, 95.2%, 70%, and 78.9 %, respectively. The efficient nitrogen removal and increased nitrate concentration signify the presence of nitrifying bacteria which actively degrade the nitrogen compounds through the nitrification process. Thus, this system is a sound alternative for both domestic and industrial wastewater treatment for decentralized applications.

Implementation of a full-scale constructed wetland to treat greywater from tourism in Suluban Uluwatu Beach, Bali, Indonesia

This original research examines a full-scale subsurface Constructed Wetland (CW) system in Indonesia, where most CW research has been limited to laboratory scale experiments. The CW system was located in Bali and built in 2015 in a single series formation. This study aims to demonstrate the performance of the system in treating greywater and examine the nutrient content plants’ above-ground biomass. The CW was arranged in linear sequence composed of one unplanted (CW1) and five planted treatments of Iris pseudacorus (CW2), Caladium bicolor (CW3), Rhoe discolor (CW4), Sansevieria trifasciata (CW5) and Heliconia psittacorum (CW6). There has been little research on Caladium bicolor, Rhoe discolor and Sansevieria trifasciata in a full-scale CW application. Our results showed fluctuating efficiency (%) in the reduction of Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Suspended Solid (TSS), Oil and Grease (O&G), Nitrate and Phosphate. The highest removal efficiency for CW1, CW2, CW3, CW4, CW5, CW6 were O&G (63.63%), BOD (90.66%), Nitrate (83.55%), BOD (80%), BOD (82.88%) and Phosphate (89.93%) respectively. After the experimental period, S. trifasciata and H. psittacorum experienced a decrease in Total N concentration, while H. psittacorum experienced a decrease in phosphate in above-ground biomass. Species of R. discolor, C. bicolor and I. pseudacorus showed good performance in terms of their growth and development. Although high removal efficiency was observed at certain times, this study showed the negative removal efficiencies at times among parameters as a consequence of the low Hydraulic Retention Time (HRT) and high Hydraulic Loading Rate (HLR).

Optimization of the wastewater treatment capacity of a short rotation willow coppice vegetation filter

The objective of this study was to determine the conditions to optimize the wastewater treatment efficiency of a short rotation willow coppice (SRWC) plantation (Salix miyabeana ‘SX67’) used as a vegetation filter to treat small municipal primary effluents (with less than 800 population equivalent). With the aim of maximizing the annual amount of wastewater treated, the effect of adjusting the hydraulic loading rate (HLR) according to the estimated evapotranspiration was tested at demonstration scale under humid continental climate conditions. We proposed a new method to calculate the evapotranspiration rate from plant physiological data, introducing an α factor based on direct transpiration measurements. This method increased the accuracy of the water balance, with a prediction of the crop coefficient (kc) based on either an seasonal approach (R2 of 0.88) or a monthly approach (R2 of 0.94). This led to a more precise estimation of the pollutant loading reaching the groundwater and could be used after plantation establishment as a fine-tuning tool. Adjusting the HLR to that of evapotranspiration between May and October led to an annual increase of 2 mm/d (around 0.35 m3/m2 per growing season) in HLR, while maintaining a pollutant loading removal efficiency of at least 96% for organic matter, 99% for total phosphorus and 93% for total nitrogen. A high HLR at the end of the season caused nitrogen leaching into groundwater, indicating that the HLR should be decreased in October, when willow growth is greatly reduced.

Influence of hydrologic conditions on nutrient retention, and soil and plant development in a former central Ohio swamp: A wetlaculture mesocosm experiment

Agricultural runoff is a major contributor of nutrients to downstream freshwater and marine waters that, in turn, cause harmful algal blooms. “Wetlaculture,” a new landscape management approach defined as “integrating wetland nutrient removal with recycling of these nutrients to agriculture,” has the dual goals of reducing the need for fertilizer in agriculture while mitigating fluxes of nutrients to downstream aquatic ecosystems with created or restored wetlands. A mesocosm compound consisted of twenty-eight 380 L, 1-m2 tubs filled with local hydric soil was initiated in mid-2016 near a highly eutrophic Buckeye Lake in central Ohio, USA, to investigate the wetlaculture approach in an experimental fashion. In October 2016, each mesocosm tub was inserted in the ground and planted with the sedge Schoenoplectus tabernaemontani. The mesocosms were assigned to four hydrologic treatments involving two water depths and two hydraulic loading rates (HLRs). Nearby river water containing significant agricultural runoff was added weekly into a water feed tank system to provide weekly hydraulic loadings to the mesocosms. Inflow and outflow water samples from each wetland mesocosm were collected and analyzed for five species of nitrogen and phosphorus. By August 2019, 17 plant species, including the planted S. tabernaemontani, were present in the wetland mesocosms. The wetland mesocosms soon became nutrient sinks with average removal efficiencies of total phosphorus (TP) and total nitrogen (TN) of 38 ± 2.5% and 44 ± 1%, respectively, through the three-year experiment. The combination of a high HLR (30 cm week−1) and 10 cm of standing water achieved the best nitrogen removal efficiencies while highest phosphorus removal occurred with the combination of a high HLR (30 cm week−1) and no standing water.This paper discusses the following integrative findings:•Seasonal flooding had positive impacts on removal efficiency of NOx and a negative impact on the removal efficiency of TP and TKN.•No standing water resulted in a higher removal efficiency of TP and TKN than standing water, results consistent with previous studies.•Macrophyte plant community richness was influenced more by water depth than by hydraulic loading rate. Wetlands with 10 cm of standing water instead of saturated soils developed lower species richness but were more dominated by true wetland (OBL and FACW) species.•Study scale does matter. Annual nutrient accumulation rates in the mesocosms (1 m2) soils were lower than in the full-scale (10,000-m2) multi-year wetlands at the nearby Olentangy River Wetland Research Park (ORWRP) in central Ohio. Annual accumulation rates of phosphorus and nitrogen in the full-scale wetlands ranged from 3.3 to 3.5 g-P m−2 yr−1 and 16.4 to 19.5 g-N m−2 yr−1, while in our mesocosms, the annual rates ranged from 0.66 to 1.40 g-P m−2 yr−1 and 7.85 to 15.08 g-N m−2 yr−1. Our experimental wetland mesocosms could only function in the non-freezing months and have been in operation for only three years.

Nitrogen removal in an aerobic gravel filtration-sedimentation pond-constructed wetland-overland flow system treating polluted stream waters: Effects of operation parameters

Nitrogen pollution in streams can be controlled by serially constructing natural wastewater treatment (NWT) systems inside streams. Therefore, a pilot-scale hybrid NWT system consisting of gravel filtration (GF), sedimentation pond (SP), gravel filtration-free water surface constructed wetland (GF-FWSCW), and gravel filtration-overland flow (GF-OF) was installed in order to prevent contamination in a stream (Nigde stream) that feeds and pollutes surface water source (Akkaya lake). The pilot-scale system was installed on a new 60 m-long channel which was located off the stream. Changes in ammonium (NH4+-N), organic nitrogen (Norg.), total nitrogen (TN), and biochemical oxygen demand (BOD) concentrations was routinely monitored in influent and effluent of all stages of the hybrid NWT system and the bottom sediment of the SP over a one-year operation period. According to the study results, while NH4+-N plus Norg. was reduced by an average of 75% (from 49,1 mg L−1 to 7,1 mg L−1), TN was reduced by an average of 85% (from 50,2 mg L−1 to 12,4 mg L−1). Colder seasons and higher hydraulic loading rates (HLRs) negatively affected nitrogen removal efficiency of the pilot-system. The use of vegetation and filter medium had a positive effect on the average removal efficiencies. The results showed that nitrogen pollution in polluted streams could be greatly reduced by establishing a NWT system in series within them.

Removal performance of high hydraulic loading rate subsurface wastewater infiltration systems with added Si[sbnd]Al porous clay material and scrap iron filings

To enhance pollutant removal performance in the treatment of decentralized domestic sewage, a subsurface wastewater infiltration system (SWIS) with turfy soil was improved by adding SiAl porous clay material W (PCMW) and scrap iron filings. The permeability at different depths of the SWIS was improved. Under the conditions of 186.18 ± 34.82 mg/L COD, 25.84 ± 2.57 mg/L NH4+-N, 3.02 ± 0.91 mg/L NO3−-N, 33.87 ± 3.78 mg/L TN, 6.93 ± 1.21 mg/L TP, a 0.28 m3/m2·d hydraulic loading rate and 716 d operation time, the average effluent concentrations of COD, NH4+-N, NO3−-N, TN and TP were 31.28 ± 5.87 mg/L, 3.39 ± 1.42 mg/L, 3.71 ± 0.87 mg/L, 7.11 ± 0.97 mg/L and 0.24 ± 0.07 mg/L, respectively, and the TN removal efficiency increased by 20.7% compared with that of the control SWIS. According to the pollutant variations with depth, 76.79% COD, 80.96% NH4+-N and 95.35% TP were removed at a depth of 110 cm, after which their concentrations remained stable; the TN concentration decreased with depth and was quite different from that of control SWIS, NH4+-N in TN was removed at a depth of 0–90 cm, and NO3−-N in TN was removed at 90–170 cm depth. Moreover, both the number of nitrifying/denitrifying bacteria and nitrate/nitrite reductase activity reached their maximum at 90 cm depth. Adding PCMW and scrap iron filings to SWISs could be an ideal method to improve the performance and service life of SWISs.

Combined biochar vertical flow and free-water surface constructed wetland system for dormitory sewage treatment and reuse

A two-stage treatment system that included vertical flow (VF) and free-water surface (FWS) constructed wetlands was investigated for the dual purposes of sewage treatment and reuse. The VF included four layers (biochar, sand, gravel, and sandy soil), and the FWS was installed after the VF and used as a polishing tank. Two types of local plants, namely Colocasia esculenta and Canna indica, were planted in the VF and FWS, respectively. The system operated for approximately six months, and the experimental period was categorized into four stages that corresponded to changes in the hydraulic loading rate (HLR) (0.02–0.12 m/d). The removal efficiencies for total suspended solids (TSS), chemical oxygen demand (COD), biological oxygen demand (BOD5), ammonia (NH4-N), and total coliform (Tcol) were 71 ± 11%, 73 ± 13%, 79 ± 11%, 91 ± 3%, and 70 ± 20%, respectively. At HLRs of 0.04–0.06 m/d, the COD and BOD5 levels satisfied Vietnam's irrigation standards, with removable rates of 64% and 88%, respectively, and the TSS and Tcol levels satisfied Vietnam's standards for potable water. Furthermore, the NO3-N levels satisfied the reuse limits, whereas the NH4-N levels exceeded the reuse standards. At high HLRs (e.g., 0.12 m/d), all the effluent parameters, except Tcol and NO3-N, exceeded the standards.

Assessing local materials for the treatment of wastewater in open drains.

In the present study, three low-cost filter aggregate materials were tested and compared for organic matter and fecal coliform (FC) removal at the laboratory scale. Setups were subjected to synthetic wastewater at two hydraulic loading rates (HLR), i.e. 4 cm/day and 40 cm/day. The hydraulic retention time (HRT) at the two HLRs varied from 4 days to 12 h, respectively. The result obtained shows that the biochemical oxygen demand (BOD5) removal efficiency of aggregate materials decreased with the increase in HLR. Both at high and low HLR, the terracotta aggregate material exhibited maximum BOD5 loading removal and without significant difference for the case of FC removal efficiency for all the three aggregate materials. At higher HLR, cell debris and biofilm loss from the aggregate material contributed to the chemical oxygen demand (COD) levels in the treated water. The terracotta aggregate material provided best organic matter removal at both HLRs. The study demonstrates the potential of incorporating inexpensive and readily available local materials into decentralized, frugal green infrastructure interventions capable of lowering the quantum of harmful biological contaminants in open storm water channels in rapidly urbanizing cities of developing countries, and that the terracotta aggregate material provided best organic removal at both HLRs.

Evaluation of Long-Term Wastewater Treatment Performances in Multi-Soil-Layering Systems in Small Rural Communities

Multi-soil-layering (MSL) wastewater treatment systems consist of soil units (soil mixture blocks, SMB) arranged in a brick-like pattern surrounded by permeable layers of zeolite or alternating particles of homogeneous sizes that allow for a high hydraulic loading rate. This study evaluated the performances of MSL systems that have been operating for 17 to 20 years in small rural communities. Even though 20 years had passed since this system was installed, high organic matter treatment performance continued. Nitrogen removal was higher than with conventional soil systems. Two of the MSL systems continued to show high phosphorus removal performances, whereas in the third system, the adsorbing capacity was relatively low, requiring further investigation. Treatment performances were largely dependent upon the structure of the MSL systems. It appeared that improving the structure to enhance the contact efficiency between the wastewater and the soil in SMB was important for enhancing treatment performances. The combined use of existing wastewater treatment systems with the MSL system was effective for preventing environmental pollution over a long period.

The Effect of Dissolved Oxygen Distribution on Ammonium Nitrogen Removal in a Pilot-Scale of Vertical Upward-Flow of Aerated Electric Arc Furnace Slag Filter Systems At Various Hydraulic Loading Rates

The performance of an aerated vertical upward-flow electric arc furnace slag filter (VFEAFS) system in treating domestic wastewater was examined in a warm-climate country temperature. Two pilot scale column experiments were conducted at high (2.72 m3/m3.day) and low (1.04 m3/m3.day) hydraulic loading rate (HLR) set-up and the effect of different hydraulic loading levels on pollutant removal efficiency were studied. Aeration was introduced in the filter system at 10 L/min to observe oxygen distribution concentration towards ammonium nitrogen removal. The results demonstrated that both HLR set-up were capable to achieve more than 90% ammonium nitrogen (AN) removal; however, in terms of individual efficiency of the filter system, the VFEAFS of lower HLR performed better in comparison to the higher HLR set-up. The average effluent concentration of AN by both systems were found far below standard A of Malaysian sewage discharge limit (10 mg NH4-N/L). The results achieved in this pilot scale study indicate that removal of ammonium nitrogen in the aerated VFEAFS was explained by nitrification process, and this treatment system could be implemented to the other industry-environmental, municipal or residential wastewater.

Application of pilot scale trickling filter couple with pre-ozonation for ammonia, iron and dissolved organic carbon removals from Saigon river water

A pilot scale trickling filter and pre-ozonation contactor with capacity of about 20 m3/day was run at Hoa Phu Pump Station which takes raw water from Saigon River for drinking water supply for Ho Chi Minh City. The raw water contains 0.52 ± 0.19 mg NH4+-N/l, 0.14 ± 0,06 mg/l total iron and 3.14 ± 0.45 mg/l DOC. The study aimed to using the pilot scale experiment to assess ammonia, iron and dissolved organic carbon (DOC) removals from Saigon Water River for the sake of reducing chlorine demand and thus mitigating risk from Disinfection By Products (DBPs) formation. The size of the trickling filter was 0.5 m long x 0.5 wide x 2m high. The bio-media was seven PE wool sheets with thickness of 30 mm that is widely used as filter cloth in aquariums. It run at hydraulic loading of 3 m3/m2.h of raw water, and 8 m3/m2.h, where 50% of total flow was the returned effluent of pre-ozonation. The pilot scale pre-ozonation contactor which has the size of 0.6 m long x 0.6 m wide x 2.0 m high was operated at contact time of 15 minutes and ozone concentration of 0.5 mg/l. The ammonia, iron and DOC removals at 8 m3/m2.h were 58%, 25% and 22%, respectively. Whereas, it obtained ammonia, iron and DOC removals of 52%, 19% and 9% DOC respectively. Thus, even though the experiment with returned pre-ozonation effluent run at high hydraulic loading rate, the better performance was obtained as comparison to the experiment without return.

Influence of hydraulic loading rate on ion precipitations and performance of a vertical-flow soil filter treating contaminated groundwater under cold climatic conditions

Long-term investigations were carried out in a pilot-scale vertical-flow soil filter (VFSF) system to characterize the fate of different precipitating ions (Fe2+, Mn2+, Ca2+) during the remediation of heavily contaminated groundwater under different hydraulic loading rates (HLRs) and to assess MTBE and BTEX removal efficiencies under low winter temperatures. Two specially designed VFSF, a roughing filter (RF) packed with expanded clay material (grain size: 3–6mm) and a polishing filter (PF) with zeolite material (grain size: 0–5mm) were operated in both single-stage and two-stage configuration. During single-stage operation, a stepwise increase of HLRs from 60 to 120, 240, 480Lm−2 d−1 in both RF and PF were applied. During two-stage operation, a highly efficient Fe2+ removal with a mean removal efficiency of 99% was already observed in the effluent of the first treatment step (RF; HLR=960Lm−2 d−1) and protected the second filter (PF; HLR=480Lm−2 d−1) from potential clogging due to iron hydroxide precipitates. The removal of Ca2+ decreased remarkably from 28% to 7% in the RF and from 54% to 10% in the PF as the HLR increased stepwise in single-stage operation. During two-stage operation with a high HLR in the RF resulted in only 3% removal of the mean Ca2+ inflow concentration (211±18mgL−1). This clearly showed that at high HLR, Ca2+ was rapidly flushing out of the VFSF system instead of carbonate precipitations and proved to be very effective to protect the filter from potential clogging. During winter, when daily mean outside air temperature was as low as −20°C, a relatively low water temperature in the range of 5.1–8°C in the effluent and a low MTBE and benzene mean removal rate of 0.41±0.07 and 2.08±0.33gm−2 d−1, respectively, was observed at a low HLR (120Lm−2 d−1). Whereas, at a high HLR (960Lm−2 d−1), a mean temperature of 13.0±1.3°C was maintained inside the filter resulting in a high MTBE and benzene removal rate of 2.37±0.02 and 14.41±0.65gm−2 d−1, respectively. Our results with high removal efficiencies for MTBE and benzene together with highly efficient Fe2+ and Mn2+ removal suggest that a two-stage VFSF can be a very promising technology for the remediation of heavily contaminated groundwater in oil and gas industries. Furthermore, it was shown that at high HLRs, filter clogging due to Ca-precipitation was prevented and treatment efficiency was not affected even under cold climate conditions with atmospheric air temperature as low as −20°C.

Comparison of pyrolucite fixed and fluidized beds for iron and manganese control in groundwater: A pilot-scale study

Iron and manganese removal is a common water treatment goal in groundwater systems. Pilot-scale pyrolucite fixed and fluidized bed contactors were tested in parallel to examine the iron and manganese removal from a natural groundwater which was supplemented with iron and manganese in order to challenge both processes. The results showed that the design of the distributor plate located at the bottom of the pyrolucite fluidized bed (PFB) contactor had crucial impact on the release of particulate manganese from the filter media. Using an optimal distributor plate, the PFB contactor provided effective manganese removal (<0.02mg/L) at very high hydraulic loading rate (45m/h). The fixed bed was also effective at 20m/h. Under elevated iron concentration (0.18±0.02mg/L), the pyrolucite fixed bed contactor alone provided almost complete iron and manganese removal while requiring frequent backwash of the filter bed (3 d). However, under such condition, the PFB contactor failed to properly control the concentration of iron and manganese below the target limit of 0.02mg/L as manganese and iron were found to be carried over in the effluent. Further study should address the potential implementation of a cost-effective post-filtration process, downstream of the PFB contactor, which would finalize the removal of iron and manganese from the PFB effluent.

Wastewater Treatment Plant Performance Inside Multi-Soil-Layering System

Wastewater effluent disposal is a challenge in Moroccan rural area. Wastewater treatment is the only suitable solution to overcome these environmental constraints. Technology such as Multi-Soil-Layering (MSL) system is one of the most appropriate solution for the treatment of wastewater for small communities in rural areas. The MSL system overcomes many of the deficiencies of conventional soil treatment systems such as large land requirement clogging and low Hydraulic Loading Rate (HLR). The MSL systems are composed of Soil Mixture Blocks (SMB) arranged in a brick-like pattern and surrounded by Permeable Layers (PL). To investigate the efficiency of MSL systems in relation to HLR differences and the fluctuations in the wastewater contamination levels, three MSL pilot plants were alimented continuously by domestic wastewater, were constructed in three 36×30×65 cm plastic boxes, with different HLR of 250, 500 and 1000 l/m2/day. The main removal rates of Biochemical Oxygen Demand (BOD5) and Chemical Oxygen Demand (COD) were higher at higher HLR. However, the kinetic rate constant of the MSL process implemented under Moroccan conditions is 130 d-1 at 25°C.