Hydraulic Residence Time Research Articles

Performance analysis of the activated sludge model (number 1)

The activated sludge process is widely used to treat both municipal sewage and a variety of industrial wastewaters. We investigate the steady-state behaviour of an activated sludge process. We use the activated sludge model number one, an internationally accepted model, to describe the biochemical, biological, and physical-chemical phenomena that occur inside the bioreactor. The treatment configuration consists of a single aerated reactor attached to a settling unit.Continuation methods are used to determine the steady-states of the model as a function of the hydraulic residence time. From these solutions we construct important operational parameters including the chemical oxygen demand, total suspended solids and total nitrogen. These are determined inside the bioreactor, in the effluent stream and in the wastage stream.We show that there are two critical values of the hydraulic retention time. As the hydraulic retention time is increased through the first critical value heterotrophic biomass become viable. This bifurcation is associated with a substantial decrease in the chemical oxygen demand in the effluent stream and a corresponding increase in both the total suspended solids and total nitrogen in the reactor. Autotrophic biomass become viable as the hydraulic retention time is increased through the second bifurcation point. Associated with this bifurcation there are dramatic changes in the concentration of soluble ammonium nitrogen and soluble nitrate/nitrite inside the reactor; the former being converted to the latter.Of particular practical interest is the value of the hydraulic retention time at which the chemical oxygen demand in the effluent stream is equal to a preset target value. We investigate how this value varies as either the composition of the influent stream or the recycle ratio is varied.

L-Erythrulose production with a multideletion strain of Gluconobacter oxydans.

Many ketoses or organic acids can be produced by membrane-associated oxidation with Gluconobacter oxydans. In this study, the oxidation of meso-erythritol to L-erythrulose was investigated with the strain G. oxydans 621HΔupp BP.8, a multideletion strain lacking the genes for eight membrane-bound dehydrogenases. First batch biotransformations with growing cells showed re-consumption of L-erythrulose by G. oxydans 621HΔupp BP.8 in contrast to resting cells. The batch biotransformation with 2.8gL-1 resting cells of G. oxydans 621HΔupp BP.8 in a DO-controlled stirred-tank bioreactor resulted in 242gL-1 L-erythrulose with a product yield of 99% (w/w) and a space-time yield of 10gL-1h-1. Reaction engineering studies showed substrate excess inhibition as well as product inhibition of G. oxydans 621HΔupp BP.8 in batch biotransformations. In order to overcome substrate inhibition, a continuous membrane bioreactor with full cell retention was applied for meso-erythritol oxidation with resting cells of G. oxydans 621HΔupp BP.8. At a mean hydraulic residence time of 2h, a space-time yield of 27gL-1h-1 L-erythrulose was achieved without changing the product yield of 99% (w/w) resulting in a cell-specific product yield of up to 4.4gPgX-1 in the steady state. The product concentration (54gL-1 L-erythrulose) was reduced in the continuous biotransformation process compared with the batch process to avoid product inhibition.

The occurrence and transformation behaviors of disinfection byproducts in drinking water distribution systems in rural areas of eastern China

The occurrence and transformation behaviors of disinfection byproducts (DBPs) were investigated in the finished water and tap water of 14 water treatment plants in rural areas of eastern China. Mammalian cell toxicity data from previous studies were used to evaluate the cytotoxicity of trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), trichloronitromethane (TCNM) and the genotoxicity of HAAs, HANs and TCNM. Correlation analysis was conducted to identify the factors that might influence the variability of DBPs. The measured median values were 29.76 μg/L for THMs, 20.47 μg/L for HAAs, 3.98 μg/L for HANs, 0.76 μg/L for haloketones (HKs) and 0.03 μg/L for TCNM. The spatial variability analysis showed that the total concentrations of HAAs and HANs decreased during long hydraulic residence time (HRT) in seven drinking water distribution systems, which could result in reduced mammalian cell cytotoxicity and genotoxicity at consumers’ taps. The concentrations of trihalogenated-DBPs were more stable than those of dihalogenated-DBPs and monohalogenated-DBPs during long HRT. Bromine acted as a more efficient substituting agent than chlorine for THMs and dihaloacetonitriles (DHANs) in actual drinking water. The dominant chlorinated-THMs and chlorinated-DHANs would transfer to brominated -THMs and brominated-DHANs when the concentration of bromide ion exceeds 450.67 and 610.25 μg/L, respectively. Correlation analysis indicated that particulate and soluble manganese (Mn) might play critical roles in promoting the production of DBPs in bulk water. Hydraulic disturbance could also result in secondary release of DBPs from loose deposits accumulated on distribution pipe walls.

Storm effects on nitrogen flux and longitudinal variability in a river–reservoir system

AbstractSustainable management of the nitrogen (N) cycle remains a considerable global challenge that has major implications for aquatic ecosystems. Dams play a critical yet often neglected role in addressing this challenge as they increase hydraulic residence time and denitrification potential. However, during storm events when the majority of N loading occurs, less is known about the effects dams have on N fate and transport processes. Here, we examined the flux of N species and phosphorus (P) and longitudinal profiles of nitrate (NO3−) along a sixth‐order river–reservoir system at baseflow and across the falling limb of a multiday, 1‐year storm hydrograph. During the storm event, the reservoir reduced total NO3− flux by 19.1% and P flux by 12.7%. On the contrary, ammonium (NH4+) fluxes were 200% higher downstream of the dam in comparison with fluxes into the reservoir, indicating that there was a substantial net export of NH4+ from the reservoir during the storm event. Longitudinally along the river to reservoir transition, a breakpoint of statistical significance was identified, highlighting the sharp contrast between NO3− concentrations within the river and reservoir. Results suggest that frequent storm events such as the one presented here can greatly alter N removal processes in river–reservoir systems. Overall, this study highlights the need to better understand the role that storm events play in river–reservoir N cycling dynamics.

Variable non-linear removal of viruses during transport through a saturated soil column

Reduction of viral surrogates (bacteriophage MS2 and murine norovirus-1 [MNV-1]) and viruses naturally present in wastewater (enteroviruses, adenoviruses, Aichi viruses, reovirus, pepper mild mottle virus) was studied in a long-term experiment simulating soil-aquifer treatment of a non-disinfected secondary treated wastewater effluent blend using a 4.4 m deep saturated soil column (95% sand, 4% silt, 1% clay) with a hydraulic residence time of 15.4 days under predominantly anoxic redox conditions. Water samples were collected over a four-week period from the column inflow and outflow as well as from seven intermediate sampling ports at different depths. Removal of MS2 was 3.5 log10 over 4.4 m and removal of MNV-1 was 3 log10 over 0.3 m. Notably, MNV-1 was removed to below detection limit within 0.3 m of soil passage. In secondary treated wastewater effluent, MNV-1 RNA and MS2 RNA degraded at a first-order rate of 0.59 day−1 and 0.12 day−1, respectively. In 15.4 days, the time to pass the soil column, the RNA-degradation of MS2 would amount to 0.8 log10, and in one day that of MNV-1 0.3 log10 implying that attachment of MNV-1 and MS2 to the sandy soil took place. Among the indigenous viruses, genome copies reductions were observed for Aichi virus (4.9 log10) and for pepper mild mottle virus (4.4 log10). This study demonstrated that under saturated flow and predominantly anoxic redox conditions MS2 removal was non-linear and could be described well by a power-law relation. Pepper mild mottle virus was removed less than all of the other viruses studied, which substantiates field studies at managed aquifer recharge sites, suggesting it may be a conservative model/tracer for enteric virus transport through soil.

Genesis of Antibiotic Resistance (AR) XLVIII: Inadequate Inactivation of Antibiotic Resistance Gene(s) (ARG) in Bio‐Sludge escalate Antibiotic Resistance Pandemic (ARP)

Inadequately and/or untreated sewage, activated sewage from the waste water treatment plants are main anthropogenic sources of Antibiotic Resistance Bacteria (ARB) encompassing ARG. Concomitant residual (sub‐therapeutic dose) of antibiotics and/or its metabolic intermediates impart a selection pressure on the ARB amending the ARGs with which modified ARB promulgate indeterminately. Implementation of following preventive measure would diminish the potential of bio sludge induced ARP: i. determine and advocate the cost effective and environmentally friendly site/location specific bioremediation method in a global context, while sustaining the processed water/clean water with 0.3 NTU/ FNU, ii. “the sludge from these hotspots should be incinerated instead of being disposal in the regular landfill”, iii. complete review of Clean Water Act, addressing the ARB with ARGs in the environment and amendment of EPA's NPDES, iv. Mandatory testing of the pre‐sewage, treated water/clean water, bio‐sludge/ bio‐solids for the levels of Lactam, sulfonamide, and tetracycline antibiotics, biocides, ARB (CFU's) and corresponding ARGs that are most frequently detected in the wastewater, v. longer hydraulic residence times in the sewage treatment process, vi. intensive research and development effort to determinant the role of bio sludge acts as metal chelate (chelater) in combination with or without fertilizer to reduce the metal toxicity to the plant, vii. determination of chlorine (gas) resistant mutant ARB across the globe in all of the sewage treatment plant & clean water, obtain the ARGs profile data and make it available online for access by academia, viii. annual report on the detection of antibiotics in the influents and effluents from WWTPs; ix. determination antibiotics, its metabolic intermediates concentration in the activated sludge and implementation of relevant antibiotic removable pathways (adsorption, biodegradation, disinfection, membrane separation, hydrolysis, photolysis and volatilization), x. determination of OTU (operational taxonomic unit) of major ARGs, sub types, in the activated sludge, comparative analysis of bacterial count at every stage of the WWTP, xi. identification of “Hot Spots”, xii. universal ban on biological waste water treatment for pharmaceutical waste water, universal adaptation of the membrane ultrafiltration technology as a pretreatment method, xiii. universal practice of incinerating the activated sludge from the “Hot Spots”, xiv. routine update of the database and annotation pipeline for the efficient analysis of the data sets available across the globe for timely data processing, xv. global report on functional screening based on the phenotype environmental sampling of the activated sludge application site and the waste water system for novel ARG, its host and associated mobile genetic elements, xvi. report on the heavy metal contamination on the activated sludge from the “Hot Spots” (environment impacted by the anthropogenic activities).Support or Funding InformationSupported by the professional development funds provided by the SWTJC to Subburaj KannanThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Design and testing of a pilot-scale submerged membrane bioreactor (MBR) for textile wastewater treatment

The objective of this paper is to deal with the design of a pilot-scale submerged membrane bioreactor (MBR) and a short-term functionality test to be performed with textile wastewater. The design calculations were done based on the design parameters analysed from local textile wastewater and typical values of activated sludge kinetic coefficients. Other process parameters like bioreactor volume (tank size), hydraulic residence time (HRT), biomass loading (F/M ratio), oxygen demand, etc., were calculated depending on the real textile wastewater characteristics. Taking the design basis into consideration, a pilot-scale MBR was constructed equipped with LabVIEW programme- and sensors-controlled computer system. Based on the theoretical calculations, the hydraulic volume of the MBR reactor was around 56.6 L with flat sheet membranes (3 sheets, with 25 cm × 25 cm dimensions of each sheet) with HRT of 16.9 h. Finally, performance tests for 6 weeks were carried out in a local (Darmstadt, Germany) laundry textile wastewater to test the functionality of MBR pilot plant. Under the operating conditions of 250 mbar suction pressure and 12 g/L of MLSS, the COD removal efficiency was around 90% for 800–3500 mg/L inlet COD fed to the membrane bioreactor.

Identification of Factors Affecting Bacterial Abundance and Community Structures in a Full-Scale Chlorinated Drinking Water Distribution System

Disentangling factors influencing suspended bacterial community structure across distribution system and building plumbing provides insight into microbial control strategies from source to tap. Water quality parameters (residence time, chlorine, and total cells) and bacterial community structure were investigated across a full-scale chlorinated drinking water distribution system. Sampling was conducted in treated water, in different areas of the distribution system and in hospital building plumbing. Bacterial community was evaluated using 16S rRNA gene sequencing. Bacterial community structure clearly differed between treated, distributed, and premise plumbing water samples. While Proteobacteria (60%), Planctomycetes (20%), and Bacteroidetes (10%) were the most abundant phyla in treated water, Proteobacteria largely dominated distribution system sites (98%) and taps (91%). Distributed and tap water differed in their Proteobacteria profile: Alphaproteobacteria was dominant in distributed water (92% vs. 65% in tap waters), whereas Betaproteobacteria was most abundant in tap water (18% vs. 2% in the distribution system). Finally, clustering of bacterial community profiles was largely explained by differences in chlorine residual concentration, total bacterial count, and water residence time. Residual disinfectant and hydraulic residence time were determinant factors of the community structure in main pipes and building plumbing, rather than treated water bacterial communities.

Impact of hydraulic residence time on nitrate removal in pilot-scale woodchip bioreactors

Nitrate (NO3−N) export from row crop agricultural systems with subsurface tile drainage continues to be a major water quality concern. Woodchip bioreactors are an effective edge-of-field practice designed to remove NO3−N from tile drainage. The NO3−N removal rate of woodchip bioreactors can be impacted by several factors, including hydraulic residence time (HRT). This study examined the impact of three HRTs, 2 h, 8 h, and 16 h, on NO3−N removal in a set of nine pilot-scale woodchip bioreactors in Central Iowa. NO3−N concentration reduction from the inlet to the outlet was significantly different for all HRTs (p < 0.05). The 16 h HRT removed the most NO3−N by concentration (7.5 mg L−1) and had the highest removal efficiency at 53.8%. The 8 h HRT removed an average of 5.5 mg L−1 NO3−N with a removal efficiency of 32.1%. The 2 h HRT removed an average of 1.3 mg L−1 NO3−N with a removal efficiency of 9.0%. The 2 h HRT had the highest NO3−N mass removal rate (MRR) at 9.0 g m−3 day−1, followed by the 8 h HRT at 8.5 g m−3 day−1, and the 16 h HRT at 7.4 g m−3 day−1, all of which were statistically different (p < 0.05). Significant explanatory variables for removal efficiency were HRT (p < 0.001) and influent NO3−N concentration (p < 0.001), (R2 = 0.80), with HRT accounting for 93% contribution. When paired with results from a companion study, the ideal HRT for the bioreactors was 8 h to achieve maximum NO3−N removal while reducing the impact from greenhouse gas emissions.

Continuous flow disinfection of WWTP secondary effluents by solar photo-Fenton at neutral pH in raceway pond reactors at pilot plant scale

The feasibility of low cost reactors such as raceway pond reactors (RPRs) for micropollutant removal as well as pathogen inactivation has recently been reported. This study presents, for the first time, the inactivation of Total Coliforms, Escherichia coli and Enterococcus sp. in WWTP secondary effluents by the solar photo-Fenton process in continuous flow at neutral pH in open reactors. Firstly, indoor assays were carried out with three hydraulic residence times (HRTs), 15, 30 and 60 min under simulated solar radiation of 30 W m−2, 5 cm liquid depth, 20 mg Fe2+ L−1 and 50 mg H2O2 L−1. At 60 and 30 min of HRT, wastewater disinfection below 1 CFU mL−1 was achieved at steady state for the three microbial groups selected. Nevertheless, at 15 min of HRT only 1-log inactivation was obtained. Taking into account the results obtained at laboratory scale, the best HRTs (60 and 30 min) were tested outdoors in 5 cm-deep RPRs in both summer and winter. The start-up began with a batch operation for 120 min with 20 mg Fe2+ L−1 and 50 mg H2O2 L−1, followed by continuous operation over three consecutive days with 20 mg Fe2+ L−1 and 30 mg H2O2 L−1 to avoid large excess of hydrogen peroxide in steady state. Bacterial inactivation results showed 30 min of HRT to be the most efficient operation condition capable of producing 305 m3 m−2 year−1 of disinfected water while complying with the Spanish Law (RD 1620/2007) for water reuse. Additionally, a reduction in iron supply ranging from 10 to 2.5 mg L−1 in continuous mode with 30 mg H2O2 L−1 was evaluated. Efficient microorganism inactivation was reached for 10 and 5 mg Fe2+ L−1, thus reducing the iron consumption at steady state four-fold. This research opens up a new line of research on the optimisation of wastewater disinfection by large-scale solar photo-Fenton.

New Integrated Self-Refluxing Rotating Biological Contactor for rural sewage treatment

Rural sewage pollution has become a serious obstacle to the development of rural areas in China. To overcome this problem, economic, efficient, stable, and low-consumption technologies are urgently needed. To this end, new equipment based on the New Integrated Self-Reflux Rotating Biological Contactor (NISRRBC) was developed for rural sewage treatment in this study. In the development process, the optimal operating parameters were determined to be 5 r/min disk rotation speed, 8 h hydraulic residence time (HRT), 40% submergence diameter of the disks (SDD), and 200% reflux ratio through orthogonal test. Then, two laboratory-scale simulations were conducted with 0% reflux as a control group and 200% reflux as a test group, and the sewage purification efficiency, sludge yield, microorganism, and microenvironment characteristics of the biofilm were investigated. The results indicated that reflux of sludge and nitrification liquid enhanced the NO3−-N concentration and biomass of NISRRBC, thereby improving the pollutant removal efficiency. Compared to 0% reflux, the removal rates of COD, SS, NH4+-N, and TN increased by 5.25 ± 4.18, 5.49 ± 0.64, 5.67 ± 2.68, and 32.63 ± 3.67%, respectively, at 200% reflux. The COD, SS, NH4+-N, and TN concentrations in the effluent were 15.34 ± 7.29, 5.32 ± 2.33, 1.70 ± 2.47, and 12.73 ± 3.94 mg/L, respectively. At 200% reflux, the biofilm formed a favorable gradient for microenvironmental conditions and functional flora, thus facilitating the removal of pollutants in sewage. The operating results of the pilot-scale NISRRBC indicate that the effluent meet the Class B Discharge standard of pollutants for municipal wastewater treatment plants (GB, 18918–2002). Overall, NISRRBC is one of the priority choices for rural sewage treatment owing to its low sludge yield, integrated design concept, and simple operation mode.

Comparison of Different Methods for Evaluating the Hydraulics of a Pilot-Scale Upflow Anaerobic Sludge Blanket Reactor

Four methods commonly used in the literature for evaluating the hydraulics of Upflow Anaerobic Sludge Blanket (UASB) reactors were compared in a pilot-scale UASB reactor (518 L). The methods are based on the analysis of the tracer concentration curve in the collection points by using ionic lithium (Li+) as a tracer. The tracer was collected at two points: in the effluent and in the sludge blanket. The methods evaluated were: (i) Qualitative analysis of the Residence Time Distribution (RTD) normalized curve (i.e., dimensionless with respect to concentration and time); (ii) empirical qualitative relations between experimental time and theoretical time by using the time-concentration tracer curve; (iii) dispersion number by using traditional equations; and (iv) dimensional axial dispersion model. The study was performed at theoretical hydraulic residence times (t0) of 600, 480, 300, 240 and 180 min. The results obtained show that the lack of criteria for defining the flow inside the reactor (plug flow, dispersed-flow or complete-mix flow) yields inconsistencies in methods (ii) and (iii). In contrast, methods (i) and (iv) are consistent with each other and can be considered as complementary. For these last two methods, it was found that there is a dispersed flow in the reactor (effluent), and a complete-mix flow in the region of the sludge bed and sludge blanket. However, method (i) is qualitative and does not relate the flow pattern with the dispersion number or Peclet number that measures the mixing magnitude or the axial dispersion in biological reactors.

Degradation of tetra- and trichloroethylene under iron reducing conditions by Acidimicrobiaceae sp. A6

The degradation of trichloroethylene (TCE) and tetrachloroethylene (PCE), in incubations where ammonium was oxidized while iron was being reduced indicates that these compounds can be degraded during the Feammox process by Acidimicrobiaceae sp. A6 (ATCC, PTA-122488). None of these compounds were degraded in incubations to which no ammonium was added, indicating that they were degraded during the oxidation of ammonium. Degradation of TCE and PCE (ranging between 32% and 55%) was observed in incubations with a pure Acidimicrobiaceae sp. A6 culture as well as an Acidimicrobiaceae sp. A6 enrichment culture over a 2-week period. In addition to these batch studies, a column study, with a 5-h hydraulic residence time, was conducted contrasting the degradation of TCE in iron-rich soil columns that were either seeded with a pure or an enrichment culture of Acidimicrobiaceae sp. A6 to achieve ammonium oxidation under iron reduction, and a control column that was initially not seeded and later seeded with Geobacter metallireducens. While there was ∼22% TCE removal in the columns seeded with Acidimicrobiaceae sp. A6, there was no removal in the unseeded column or the column seeded with G. metallireducens which was being operated under iron reducing conditions. Feammox is an anoxic process that requires acidic conditions. Hence, these results indicate that this process might be harnessed where other bioremediation strategies are difficult, since many require neutral or alkaline conditions, and supplying ammonium to an anoxic aquifer is relatively easy, since there are not many processes that will oxidize ammonium in the absence of dissolved oxygen.

Hydrophysical and Hydrochemical Controls of Cyanobacterial Blooms in Coursey Pond, Delaware (USA).

Noxious cyanobacterial blooms are common in many ponds in the mid-Atlantic Coastal Plain. In Delaware, blooms normally occur between July and October, yet no in-depth analyses of the causes and predictors exist. A study using commercially available, high-frequency, continuous, and automated biogeochemical sensors at Coursey Pond, Delaware, a pond known for perennial summer blooms, was conducted to investigate how hydrophysical and hydrochemical conditions affect bloom dynamics. Cyanobacterial abundance (based on the in vivo phycocyanin fluorescence and phycocyanin/chlorophyll fluorescence ratios) increases during periods of high water temperatures (up to 32°C), low discharge through the pond (mean hydraulic residence time ≥5 d) with evaporative concentration of dissolved solids, and decreasing NO concentrations (reaching <0.1 mg L, the detection limit). These conditions lead to the uptake and depletion of bioavailable N in the pond surface waters and provide a competitive advantage for temperature-tolerant and N-fixing cyanobacteria. Irrigation water use within the watershed can exceed pond discharge during drier summer months, enhancing bloom-forming conditions. Bloom intensity varies due to storms but persists until mid-October to mid-November when temperatures cool, daylength decreases, and discharge and NO concentration recovers. Changes in these easily monitored physical and chemical parameters can serve to anticipate the onset, intensity, persistence, and the eventual dissipation of cyanobacterial blooms at Coursey Pond and similar ponds elsewhere. Therefore, the use of sensors and high-frequency data has the potential to assist in forecasting and management of blooms.

Hydrology and Hydraulics of the Lubigi Wetland in Uganda

The Lubigi wetland, which is located in the north-western part of Kampala, receives polluted water from Kampala city and discharges it into Mayanja River. However, there is lack of information and knowledge on the hydrology and hydraulics of the Lubigi wetland, which are important for protection of wetland ecosystems and fulfill the Uganda national policy for the conservation and management of wetland resources. The national policy aims at promoting the conservation of Uganda’s wetlands, in order to sustain their ecological and socio-economic functions for the present and future well- being of all the people of Uganda. Pertinent data collection, field tests and surveys were carried out to gather data necessary for establishing the current status of the hydraulics and hydrology of Lubigi wetland. The results revealed that the Lubigi wetland demonstrates considerable impounding reservoir and flood buffering capacity. This is an important service provided by the wetland, to alleviate possible negative impacts of storms and floods events. The Lubigi wetland total influents and effluents discharges, have mean values of 222,377.60±132,365 m3 /day and 221,356.80±122,256 m3 /d, respectively. The wetland water balance is dominated by the influent discharges which account for 93.21% of the total water influx, and the effluent discharges which account for 97.7% of the total water outflow. The wetland main study area hydraulic residence times, varies between 6.0 hours and 10 days. Hence, the wetland is endowed with abundant water fluxes, water impounding capacity and adequate hydraulic retention times. The volumetric efficiency of the wetland main study area is 63% and 38% during wet season and dry season, respectively. This indicates that on average only about 50% of the volume of the Lubigi wetland main study area is lost through short-circuiting. The dispersion number of the wetland was about 0.01 to 0.03, which indicates that the flow regime through wetland is close to plug flow.

Baffling efficiency insights gained from tracer studies at 32 Washington treatment plants

This article summarizes tracer studies performed at 32 water treatment plants in Washington State ranging from 5 to 5,400 gpm, with contact basins from 200 gal to 1.5 mil gal. Multiple tracer studies were performed at each plant. The goal of the tracer studies was to determine the baffling efficiency (BE) of each basin by determining T10/T, where T10 is the time at which 10% of a tracer is measured at the outlet of a basin, and T is the hydraulic residence time. The tracer studies indicated that most facilities historically used BE values higher than what the tracer studies indicated for calculating compliance with disinfection regulations. The majority of the basins were rectangular, baffled basins. The tracer studies indicated that standard design parameters, such as length‐to‐width ratio, were not as accurate in predicting basin performance compared with calculating baffled channel cross‐sectional velocity. This effect was pronounced where cross‐sectional flow velocity was below the Reynolds laminar flow threshold. For circular, baffled basins, a relationship between cross‐sectional velocity and BE was also evident. The study also identified issues with plants having parallel, chlorine contact basins where uneven flow splitting between basins created an overall system BE less than the BE of individual basins.

Biochar fails to enhance nutrient removal in woodchip bioreactor columns following saturation

Denitrifying bioreactors are edge-of-field structures that remove excess nitrogen (N) from intercepted agricultural drainage by supporting the activity of denitrifying microorganisms with a saturated organic carbon substrate. Although these bioreactors successfully mitigate N export, the typical woodchip systems have little effect on phosphorus (P), which is also often present in environmentally harmful quantities in drainage waters. Currently, the evidence that amending woodchip bioreactors with biochar enhances both N and P removal rates is mixed, but more work is required to test this hypothesis under controlled conditions. To determine the effect of biochar amendment on nitrate (NO3-N) and phosphate (PO4-P) removal in woodchip bioreactors, three media types—aged woodchips (W), 10% (B10) and 30% (B30) biochar by volume—were tested under different operational conditions during five-day laboratory trials with horizontal, flow-through columns. Nutrient removal was observed under different flow rates yielding hydraulic residence times of 3, 6, and 12 hours with four formulations of simulated agricultural drainage, all combination of 16.1 or 4.5 mg L−1 NO3-N and 1.9 or 0.6 mg L−1 PO4-P. Each unique treatment with respect to media type, HRT, and influent formulation was tested in triplicate using independent columns. All treatments successfully removed NO3-N, but PO4-P removal was inconsistent. Cumulative NO3-N removal efficiencies ranged 15–98% with an average removal rate of 11.0 g m−3 d−1; biochar amendment enhanced removal only in response to sufficiently high loading rates. Cumulative PO4-P removal efficiencies ranged from 66% removal to 170% export of the influent load; biochar addition was associated with increased export. These results indicate that pine-feedstock biochar poses a substantial increase to PO4-P leaching risk and only modestly enhances NO3-N removal given sufficiently high loading.

Analysis of swale factors implicated in pollutant removal efficiency using a swale database

Swales are traditional basic open-drainage systems which are able to remove stormwater-borne pollutants. In spite of numerous case studies devoted to their performances, parameters influencing the reduction of pollutant concentrations by swales remain elusive. In order to better characterize them, a database was set up by collecting performance results and design characteristics from 59 swales reported in the literature. Investigations on correlations among pollutant efficiency ratios (ERs) indicated that total trace metals (copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb)), total suspended solids (TSS), total phosphorus (TP), and total Kjeldahl nitrogen (TKN) exhibited many cross-correlated ERs. High ERs were observed for pollutants including a particulate form such as TSS (median ERs = 56%) and total trace metals (median ERs ≥ 62%), suggesting that these pollutants are efficiently trapped by sedimentation in swale bed and/or filtered within swale soil. Medium to high ERs were found for dissolved trace metals (median ERs ≥ 44%), whereas ERs for nutrient species were lower (median ERs ≤ 30%). The inflow concentration was identified as a major factor correlated to ER for most pollutants. For some pollutants, there is also a trend to get higher ER when the geometrical design of the swale increases the hydraulic residence time. Overall, this database may help to better understand swale systems and to optimize their design for improving pollutant removal.

Stratification of microbial communities throughout a biological sulphate reducing up-flow anaerobic packed bed reactor, revealed through 16S metagenomics

Biological sulphate reduction (BSR) is a promising low-cost treatment of acid rock drainage effluents. In this paper, the system performance and microbial ecology of a lactate supplemented BSR up-flow anaerobic packed bed reactor (UAPBR) are evaluated across reactor height and compared to a continuous stirred tank reactor (CSTR). The biomass concentrations of planktonic and biofilm communities were quantified and subsequently characterised by 16S rRNA gene amplicon sequencing. The defined microbial communities were shown to correlate with differing availability of lactate, volatile fatty acids produced from lactate degradation and sulphate concentration. The UAPBR was able to achieve near complete sulphate conversion at a 4-day hydraulic residence time (HRT) at a sulphate feed concentration of 10.41 mM (1 g/L). The high volumetric sulphate reduction rate of 0.184 mM/L.h achieved in the first third of the reactor was attributed to OTUs present in the planktonic and biofilm communities. While the scavenging of sulphate within the final third of the UAPBR was attributed to an acetate oxidising genus of SRB which was not detected in the lactate-fed CSTR. The detailed analyses of the microbial communities throughout the UAPBR and CSTR contribute to the growing understanding of the impact of the microbial communities of BSR reactors on system performance.

Residence time distribution in rapid multiphase reactors

Residence time distribution (RTD) provides information about average hydraulic residence time and the distribution of material in the reactor. A method for determining RTD for reactors with very short hydraulic residence times is deconvolution based on extraction of real RTD by the analysis of a non-ideal input signal. The mean residence time and dispersion were determined for the spinning fluids reactor (SFR). For the first time the deconvolution method was performed for a system where the tracer pulse signal is wider than actual RTD of the examined device. A prediction model for of the SFR was also developed, and validated.