Long term operation of pilot-scale biological nutrient removal process in treating municipal wastewater

The performance of a pilot-scale biological nutrient removal process has been evaluated for 336 days, receiving the real municipal wastewater with a flowrate of 6.8 m³/d. The process incorporated an intermittent aeration reactor for enhancing the effluent quality, and a nitrification reactor packed with the porous polyurethane foam media for supporting the attached-growth of microorganism responsible for nitrification. The observation shows that the process enabled a relatively stable and high performance in both organics and nutrient removals. When the SRT was maintained at 12 days, COD, nitrogen, and phosphorus removals averaged as high as 89% at a loading rate of 0.42–3.95 kg COD/m³ d (corresponding to average influent concentration of 304 mg COD/L), 76% at the loading rate of 0.03–0.27 kg N/m³ d (with 37.1 mg TN/L on average), and 95% at the loading rate of 0.01–0.07 kg TP/m³ d (with 5.4 mg TP/L on average), respectively.     

Leachate treatment and greenhouse gas emission in subsurface horizontal flow constructed wetland

Organic and nitrogen removal efficiencies in subsurface horizontal flow wetland system (HSF) with cattail (Typha augustifolia) treating young and partially stabilized solid waste leachate were investigated. Hydraulic loading rate (HLR) in the system was varied at 0.01, 0.028 and 0.056 m³/m² d which is equivalent to hydraulic retention time (HRT) of 28, 10 and 5 d. Average BOD removals in the system were 98% and 71% when applied to young and partially stabilized leachate at HLR of 0.01 m³/m² d. In term of total kjeldahl nitrogen, average removal efficiencies were 43% and 46%. High nitrogen in the stabilized leachate adversely affected the treatment performance and vegetation in the system. Nitrogen transforming bacteria were found varied along the treatment pathway. Methane emission rate was found to be highest at the inlet zone during young leachate treatment at 79–712 mg/m² d whereas CO₂ emission ranged from 26–3266 mg/m² d. The emission of N₂O was not detected.     

Evaluation of passive solar heating and alternative flow regimes on nitrate removal in denitrification beds

Denitrification beds are a simple and relatively inexpensive technology for removing nitrate from point source discharges. To date, operational beds have used wood media as the carbon source, as it provides a sustained nitrate removal rate (2-10 g N m⁻³ of media d⁻¹) while maintaining permeability. In pilot-scale (2.9 m⁻³) denitrification beds receiving municipal wastewater effluent dosed with KNO₃, we looked at improving nitrate removal by using alternative carbon media (maize cobs) and increasing bed temperature through passive solar heating. The influence of flow regime (horizontal-point, horizontal-diffuse, downflow and upflow) on short-circuit flow was also investigated.The long-term nitrate removal rate (21.8 g N m⁻³ d⁻¹) of the maize cob beds over the 15-month period of the trial was 2-11-fold higher than sustained removal rates reported by other researchers for wood-based beds. While passive solar heating raised the mean bed temperature by 3.4 °C, it did not cause a measurable increase in the nitrate removal rate due to the variability in the removal rate exceeding the expected increase due to temperature.Horizontal flow had more short-circuiting than vertical flow. Short-circuiting in the horizontal flow was attributed to flow being concentrated near the top surface due to the buoyancy effect of warmer water. Greater short-circuiting in the solar heated horizontal and upflow beds than in the corresponding unheated beds was attributed to the buoyancy effect being more pronounced in the solar heated beds.Overall, downflow was deemed the most effective of the four tested flow regimes. It provided the highest increase in bed temperature due to solar heating, had the highest nitrate removal rate in the latter part of the trial and had more plug-flow characteristics. While passive solar heating raised bed temperature, we were unable to demonstrate a significant difference (at 95% CL) in nitrate removal rate between the unheated and solar heated beds because of the high variability in nitrate removal rate and the increase in short-circuiting in the solar heated horizontal and upflow beds.     

The role of loading rate, backwashing, water and air velocities in an up-flow nitrifying tertiary filter

The vertical distribution of nitrification performances in an up-flow biological aerated filter operated at tertiary nitrification stage is evaluated in this paper. Experimental data were collected from a semi-industrial pilot-plant under various operating conditions. The actual and the maximum nitrification rates were measured at different levels inside the up-flow biofilter. A nitrogen loading rate higher than 1.0 kg NH₄-N m⁻³_media d⁻¹ is necessary to obtain nitrification activity over all the height of the biofilter. The increase in water and air velocities from 6 to 10 m h⁻¹ and 10 to 20 m h⁻¹ has increased the nitrification rate by 80% and 20% respectively. Backwashing decreases the maximum nitrification rate in the media by only 3-14%. The nitrification rate measured at a level of 0.5 m above the bottom of the filter is four times higher than the applied daily average volumetric nitrogen loading rate up to 1.5 kg NH₄-N m⁻³_media d⁻¹. Finally, it is shown that 58% of the available nitrification activity is mobilized in steady-state conditions while up to 100% is used under inflow-rate increase.     

Evaluation of a lab-scale tidal flow constructed wetland performance: Oxygen transfer capacity, organic matter and ammonium removal

Oxygen transfer capacity and removal of ammonium and organic matter were investigated in this study to evaluate the performance of a lab-scale tidal flow constructed wetland. Average oxygen supply under tidal operation (350 g m⁻² d⁻¹) was much higher than in conventional constructed wetlands (<100 g m⁻² d⁻¹), resulting in enhanced removal of BOD₅ and NH₄⁺. Theoretical oxygen demand from BOD₅ removal and nitrification was approximately matched by the measured oxygen supply, which indicated aerobic consumption of BOD₅ and NH₄⁺ under tidal operation. When BOD₅ removal increased from 148 g m⁻² d⁻¹ to 294 g m⁻² d⁻¹, neither exhausted oxygen from the aggregate matrix during feeding period (111 g m⁻² d⁻¹) nor effluent dissolved oxygen (DO) concentration (2.8 mg/L) changed significantly, demonstrating that the oxygen transfer potential of the treatment system had not been exceeded. However, even though DO had not been exhausted, inhibition of nitrification was observed under high BOD loading. The loss of nitrification was attributed to excessive heterotrophic biofilm growth believed to induce oxygen transfer limitations or oxygen competition in thickened biofilms.     

Reduction of ammonia and volatile organic compounds from food waste-composting facilities using a novel anti-clogging biofilter system

The performance of a pilot-scale anti-clogging biofilter system (ABS) was evaluated over a period of 125 days for treating ammonia and volatile organic compounds emitted from a full-scale food waste-composting facility. The pilot-scale ABS was designed to intermittently and automatically remove excess biomass using an agitator. When the pressure drop in the polyurethane filter bed was increased to a set point (50 mm H₂O m⁻¹), due to excess biomass acclimation, the agitator automatically worked by the differential pressure switch, without biofilter shutdown. A high removal efficiency (97-99%) was stably maintained for the 125 days after an acclimation period of 1 week, even thought the inlet gas concentrations fluctuated from 0.16 to 0.55 g m⁻³. Due the intermittent automatic agitation of the filter bed, the biomass concentration and pressure drop in the biofilter were maintained within the ranges of 1.1-2.0 g-DCW g PU⁻¹ and below 50 mm H₂O m⁻¹, respectively.     

Ammonia removal from a waste air stream using a biotrickling filter packed with polyurethane foam through the SND process

This paper presents the results of a bench-scale biotrickling filter (BTF) on the removal of ammonia gas from a waste stream using a simultaneous nitrification/denitrification (SND) process. It was found that the developed BTF could completely remove 100 ppm ammonia from a waste stream, with an empty bed retention time of 60 s and 98.4% nitrogen removal through the SND process under the tested conditions. It was elucidated that both autotrophic and heterotrophic bacteria were involved in the nitrogen removal trough the SND process in the BTF. Additionally, the elimination capacity of total nitrogen by the BTF increased from 3.5 to 18.4 g N/m³ h with an inlet load of 20.6 g N/m³ h (73.6%). The findings of this study suggest that the BTF can be operated to attain complete ammonia removal through the SND process, thereby making the treatment of ammonia-laden gas streams both short and cost-effective.     

Development of a simultaneous partial nitrification and anaerobic ammonia oxidation process in a single reactor

Up-flow oxygen-controlled biofilm reactors equipped with a non-woven fabric support were used as a single reactor system for autotrophic nitrogen removal based on a combined partial nitrification and anaerobic ammonium oxidation (anammox) reaction. The up-flow biofilm reactors were initiated as either a partial nitrifying reactor or an anammox reactor, respectively, and simultaneous partial nitrification and anammox was established by careful control of the aeration rate. The combined partial nitrification and anammox reaction was successfully developed in both biofilm reactors without additional biomass inoculation. The reactor initiated as the anammox reactor gave a slightly higher and more stable mean nitrogen removal rate of 0.35 (± 0.19) kg-N m⁻³ d⁻¹ than the reactor initiated as the partial nitrifying reactor (0.23 (± 0.16) kg-N m⁻³ d⁻¹). FISH analysis revealed that the biofilm in the reactor started as the anammox reactor were composed of anammox bacteria located in inner anoxic layers that were surrounded by surface aerobic AOB layers, whereas AOB and anammox bacteria were mixed without a distinguishable niche in the biofilm in the reactor started as the partial nitrifying reactor. However, it was difficult to efficiently maintain the stable partial nitrification owing to inefficient aeration in the reactor, which is a key to development of the combined partial nitrification and anammox reaction in a single biofilm reactor.     

Chlorobenzene removal efficiencies and removal processes in a pilot-scale constructed wetland treating contaminated groundwater

Low-chlorinated benzenes (CBs) are widespread groundwater contaminants and often threaten to contaminate surface waters. Constructed wetlands (CWs) in river floodplains are a promising technology for protecting sensitive surface water bodies from the impact of CBs. The efficiency and seasonal variability of monochlorobenzene (MCB), 1,4-dichlorobenzene (1,4-DCB) and 1,2-dichlorobenzene (1,2-DCB) removal, the impact of planting, and gaseous MCB emissions from the filter surface were investigated over the course of 1 year in both a vegetated pilot-scale CW and an unplanted reference plot (UR). Annual mean concentration decreases of MCB and 1,4-DCB were observed; however, annual mean 1,2-DCB removal was seen only in the upper filter layer. Planting (Phragmites australis) had a statistically significant beneficial effect on removal. The CB removal efficiency in the CW generally decreased with depth, and seasonal variations of removal were evident, with less concentration decrease during summer. Load removal efficiencies of 59-65% (262-358 mg m⁻² d⁻¹) for MCB, 59-69% (4.0-5.1 mg m⁻² d⁻¹) for 1,4-DCB and 29-42% (0.6-2.1 mg m⁻² d⁻¹) for 1,2-DCB were observed in June and July. Volatilization of MCB from the filter surface accounted for 2-4% of the total amount removed. Simple cover layers of organic materials on the filter surface were suitable for MCB emission reduction. Model calculations were carried out to estimate the MCB removal potential attributable to microbial degradation, volatilisation, and plant uptake in the CW and UR. Microbial degradation was the dominating process. The observed positive impact of plants on MCB removal was caused by improved oxygen supply (due to root oxygen release into the rhizosphere and enhanced water table fluctuations), and direct plant uptake.     

Horizontal or vertical photobioreactors? How to improve microalgae photosynthetic efficiency

The productivity of a vertical outdoor photobioreactor was quantitatively assessed and compared to a horizontal reactor. Daily light cycles in southern Spain were simulated and applied to grow the microalgae Chlorella sorokiniana in a flat panel photobioreactor.The maximal irradiance around noon differs from 400 μmol photons m⁻² s⁻¹ in the vertical position to 1800 μmol photons m⁻² s⁻¹ in the horizontal position. The highest volumetric productivity was achieved in the simulated horizontal position, 4 g kg culture⁻¹ d⁻¹. The highest photosynthetic efficiency was found for the vertical simulation, 1.3 g of biomass produced per mol of PAR photons supplied, which compares favorably to the horizontal position (0.85 g mol⁻¹) and to the theoretical maximal yield (1.8 g mol⁻¹). These results prove that productivity per unit of ground area could be greatly enhanced by placing the photobioreactors vertically.     

Effects of hydraulic loading rate on pollutants removal by a deep subsurface wastewater infiltration system

The subsurface wastewater infiltration (SWI) system proved to be an effective and low-cost technique for decentralized sewage treatment in areas without adequate domestic treatment facilities. Field-scale experiments were conducted through a deep SWI system, with effective depth of 1.5 m, under hydraulic loading rates of 0.040, 0.065, 0.081 and 0.10 m³/m² d. Taking the hydraulic and treatment efficiencies into consideration, the hydraulic loading rate of 0.081 m³/m² d was recommended. Under this condition, NH₃-N, TN, and COD removal efficiencies were 86.2 ± 3.0, 80.7 ± 1.9 and 84.8 ± 2.1%, respectively. In the effluent, NH₃-N concentration declined to 2.3-4.4 mg/L, accounting for 63.2-65.6% of TN. NO₃-N concentration increased from 0.2 to 0.3 mg/L in the influent to 2.0-2.5 mg/L in the effluent. The nitrifying bacteria number declined with increased depth, while the amount of denitrifying bacteria increased. The analysis of results about the nitrifying and denitrifying bacteria distribution indicated that the most effective ranges for nitrification and denitrification process were 0.3-0.7 m and 0.7-1.5 m, respectively.     

Treatment of olive mill wastewater in pilot-scale vertical flow constructed wetlands

Pilot-scale constructed wetlands (CW) were constructed and operated to treat pre-treated olive mill wastewater. Pilot-scale units comprising three identical series with four pilot-scale vertical flow CWs were operated for one harvest season in a Greek olive mill plant. The pilot-scale CWs were filled with various porous media (i.e., cobble, gravel, and sand) of different gradations. Two series of pilot-scale units were planted with common reeds and the third (control) was unplanted. Mean influent concentrations were 14,120 mg/L, 2841 mg/L, 95 mg/L, 123 mg/L and 506 mg/L for COD, phenols, ortho-phosphate, ammonia and TKN, respectively. Despite the rather high influent concentrations, the performance of the CW units was very effective since it achieved removals of about 70%, 70%, 75% and 87% for COD, phenols, TKN and ortho-phosphate, respectively. COD, phenol and TKN removal seems to be significantly higher in the planted series, while ortho-phosphate removal shows no significant differences among the three series. Temperature and pollutant surface load seem to affect the removal efficiency of all pollutants. Compared to previous studies, pollutant surface loads applied here were higher (by one or two orders of magnitude). Even though high removal efficiencies were achieved, effluent pollutant concentrations remained high, thus preventing their use for irrigation or immediate disposal into the environment.     

Pre-acclimation of a wastewater inoculum to cellulose in an aqueous-cathode MEC improves power generation in air-cathode MFCs

Cellulose has been used in two-chamber microbial fuel cells (MFCs), but power densities were low. Higher power densities can be achieved in air-cathode MFCs using an inoculum from a two-chamber, aqueous-cathode microbial electrolysis cell (MEC). Air-cathode MFCs with this inoculum produced maximum power densities of 1070 mW m⁻² (cathode surface area) in single-chamber and 880 mW m⁻² in two-chamber MFCs. Coulombic efficiencies ranged from 25% to 50%, and COD removals were 50-70% based on total cellulose removals of 60-80%. Decreasing the reactor volume from 26 to 14 mL (while maintaining constant electrode spacing) decreased power output by 66% (from 526 to 180 mW m⁻²) due to a reduction in total mass of cellulose added. These results demonstrate that air-cathode MFCs can produce high power densities with cellulose following proper acclimation of the inoculum, and that organic loading rates are important for maximizing power densities from particulate substrates.     

Aerobic granular sludge formation for high strength agro-based wastewater treatment

The present study investigates the formation of aerobic granular sludge in sequencing batch reactor (SBR) fed with palm oil mill effluent (POME). Stable granules were observed in the reactor with diameters between 2.0 and 4.0 mm at a chemical oxygen demand (COD) loading rate of 2.5 kg COD m⁻³ d⁻¹. The biomass concentration was 7600 mg L⁻¹ while the sludge volume index (SVI) was 31.3 mL g SS⁻¹ indicating good biomass accumulation in the reactor and good settling properties of granular sludge, respectively. COD and ammonia removals were achieved at a maximum of 91.1% and 97.6%, respectively while color removal averaged at only 38%. This study provides insights on the development and the capabilities of aerobic granular sludge in POME treatment.     

Biofiltration of reduced sulphur compounds and community analysis of sulphur-oxidizing bacteria

The present work aims to use a two-stage biotrickling filters for simultaneous treatment of hydrogen sulphide (H₂S), methyl mercaptan (MM), dimethyl sulphide (DMS) and dimethyl disulphide (DMDS). The first biofilter was inoculated with Acidithiobacillus thiooxidans (BAT) and the second one with Thiobacillus thioparus (BTT). For separate feeds of reduced sulphur compounds (RSC), the elimination capacity (EC) order was DMDS > DMS > MM. The EC values were 9.8 g_MM-S/m³/h (BTT; 78% removal efficiency (RE); empty bed residence time (EBRT) 58 s), 36 g_DMDS-S/m³/h (BTT; 94.4% RE; EBRT 76 s) and 57.5 g_H2S-S/m³/h (BAT; 92% RE; EBRT 59 s). For the simultaneous removal of RSC in BTT, an increase in the H₂S concentration from 23 to 293 ppmv (EBRT of 59 s) inhibited the RE of DMS (97-84% RE), DMDS (86-76% RE) and MM (83-67% RE). In the two-stage biofiltration, the RE did not decrease on increasing the H₂S concentration from 75 to 432 ppmv.     

Seasonal productivity of a periphytic algal community for biofuel feedstock generation and nutrient treatment

Algal biomass is a promising feedstock for biofuel production. With a high lipid content and high rate of production, algae can produce more oil on less land than traditional bioenergy crops. Algal communities can also be used to remove nutrients from impacted waters. The purpose of this study was to demonstrate the ability of an algal turf scrubber (ATS)™ to facilitate the growth of periphytic algal communities for the production of biomass feedstock and the removal of nutrients from a local stream. A pilot-scale ATS was implemented in Springdale, AR, and operated over the course of a nine-month sampling period. System productivity over the nine-month operating time averaged 26 g m⁻² d⁻¹. Total phosphorus and total nitrogen removal averaged 48% and 13%, respectively. The system showed potential for biomass generation and nutrient removal across three seasons.     

Nitrogen mass balances for pilot-scale biofilm stabilization ponds under tropical conditions

Nitrogen removal in biofilm waste stabilization ponds were modeled using nitrogen mass balance equations. Four pilot-scale biofilm maturation ponds were constructed in Uganda. Pond 1 was control; the others had 15 baffles in each of them. Two loading conditions were investigated (period 1, 18.2 g and period 2, 26.8 g NH₄-N d⁻¹). Total nitrogen and TKN mass balances were made. Bulk water and biofilm nitrification rates were determined and used in the TKN mass balance. Results for total nitrogen mass balance showed that for both periods, denitrification was the major removal mechanism. Nitrogen uptake by algae was more important during period 1 than in period 2. The TKN mass balance predicted well effluent TKN for period 2 than period 1. This could be due to fluctuations in algae density and ammonia uptake during period 1, no conclusions on reliability of mass balance model in period 1 was made.     

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.