High Hydraulic Loading Rate Research Articles

Phylogenetic characterization of microbial communities in a full-scale vermifilter treating rural domestic sewage

A full-scale vermifilter (VF) system was conducted and applied to treat rural domestic sewage caused by water pollution in China. The performance of full-scale VF and the microbial communities were investigated. Results showed that the average removal efficiency of COD, BOD5, NH4+N, and TSS were 67.6%, 78.0%, 92.1%, and 89.8%, respectively, with low sludge production of 0.08kgSS/kg CODremoved during 17-month operation of VF, and the final effluent could meet the latest standards of irrigation water quality in China. Phylogenetic analysis of 16S rRNA gene sequences revealed that VF was dominated by Proteobacteria, especially the γ-proteobacteria, followed by Acidobacteria, Bacteroidetes, and Planctomycetes. Most of these phyla are known to utilize a wide spectrum of carbon and nitrogen sources, or to resist a high hydraulic loading rate. Numerically minor but functionally relevant community constitutes were also detected, such as Gemmatimonadetes, Verrucomicrobia, Actinobacteria, and Chloroflexi. Earthworm activity, which causes sludge reduction of the VF, had a significant impact on the microbial population because of special microbes related to earthworm gut- and cast-associated processes that were abundant in VF biofilms. These results highlight the stability and the diverse microbial communities of full-scale VF under real operating conditions. This study is an essential first step to improving the design and operation of VF systems for practical application in domestic sewage treatment.

Feasibility of constructed wetland planted with Leersia hexandra Swartz for removing Cr, Cu and Ni from electroplating wastewater

As a low-cost treatment technology for effluent, the constructed wetlands can be applied to remove the heavy metals from wastewater. Leersia hexandra Swartz is a metal-accumulating hygrophyte with great potential to remove heavy metal from water. In this study, two pilot-scale constructed wetlands planted with L. hexandra (CWL) were set up in greenhouse to treat electroplating wastewater containing Cr, Cu and Ni. The treatment performance of CWL under different hydraulic loading rates (HLR) and initial metal concentrations were also evaluated. The results showed that CWL significantly reduced the concentrations of Cr, Cu and Ni in wastewater by 84.4%, 97.1% and 94.3%, respectively. High HLR decreased the removal efficiencies of Cr, Cu and Ni; however, the heavy metal concentrations in effluent met Emission Standard of Pollutants for Electroplating in China (ESPE) at HLR less than 0.3 m3/m2 d. For the influent of 5 mg/L Cr, 10 mg/L Cu and 8 mg/L Ni, effluent concentrations were below maximum allowable concentrations in ESPE, indicating that the removal of Cr, Cu and Ni by CWL was feasible at considerably high influent metal concentrations. Mass balance showed that the primary sink for the retention of contaminants within the constructed wetland system was the sediment, which accounted for 59.5%, 83.5%, and 73.9% of the Cr, Cu and Ni, respectively. The data from the pilot wetlands support the view that CWL could be used to successfully remove Cr, Cu and Ni from electroplating wastewater.

Empirical regression models for estimating nitrogen removal in a stormwater wetland during dry and wet days

Due to the highly variable hydrologic quantity and quality of stormwater runoff, which requires more complex models for proper prediction of treatment, a relatively few and site-specific models for stormwater wetlands have been developed. In this study, regression models based on extensive operational data and wastewater wetlands were adapted to a stormwater wetland receiving both base flow and storm flow from an agricultural area. The models were calibrated in Excel Solver using 15 sets of operational data gathered from random sampling during dry days. The calibrated models were then applied to 20 sets of event mean concentration data from composite sampling during 20 independent rainfall events. For dry days, the models estimated effluent concentrations of nitrogen species that were close to the measured values. However, overestimations during wet days were made for NH(3)-N and total Kjeldahl nitrogen, which resulted from higher hydraulic loading rates and influent nitrogen concentrations during storm flows. The results showed that biological nitrification and denitrification was the major nitrogen removal mechanism during dry days. Meanwhile, during wet days, the prevailing aerobic conditions decreased the denitrification capacity of the wetland, and sedimentation of particulate organic nitrogen and particle-associated forms of nitrogen was increased.

Nitrate removal from tail water by integrated vertical-flow constructed wetlands at a high hydraulic loading rate

Nitrate removal rates of two pilot-scale integrated vertical-flow constructed wetlands (IVCWs) treating tail water, under a hydraulic loading rate (HLR) of 250 mm/d with a mean influent NO3--N concentration of 24.4 mg.L-1, were evaluated. Mean NO3--N removal efficiencies of 15.5 and 18.5% with mass removal rates of 1.01 g.m(-2).d(-1) and 1.16 g.m(-2).d(-1) for IVCW 1 (planted with Canna indica and Pontederia cordata) and 2 (planted with Typha orientalis and Arundo donax var. versicolor), respectively, were achieved. The removal rate constants as fitted by the first-order area-based model averaged 0.046 and 0.055 m.d(-1), respectively. Since NO3--N was the dominant nitrogen form in the effluent, denitrification was the limiting step in nitrogen removal despite of favorable pH and anaerobic conditions in the wetland beds. Low availability of carbon source, high HLR, and low temperature could be the probable influencing factors for the observed low NO3--N removal efficiencies. However, IVCW could be used to treat tail water for nitrate removal at a comparable high loading rate.

Effects of porosity on flow of free water surface constructed wetland in a physical model

Despite the widespread use of constructed wetland, the parameters of its design and their operational related parameters have not yet been clearly defined. In free water surface (FWS) flow constructed wetland (CW), emergent vegetation is a primary component in pollutant removals that alters the porosity and flow pattern of water. Based on tracer experiments in a physical model, this study investigates how porosity affects hydraulic performance parameters. Experimental results indicate that, at a rather low hydraulic loading rate (HLR), the mean residence time (τm) decreases with decreasing porosity (ϵ). When the static and dynamic effects are balanced, the relation between ϵ and τm becomes neutral at a high HLR. However, the Reynolds number (NR) can accurately predict τm. A rather high coefficient of multiple determination for the proposed model is 0.985. This study also investigates, how the number of tanks-in-series (N) under various porosities influences the flow pattern. When vegetation is lacking, N ranges from 1.27 to 1.94. With an increasing HLR, the flow pattern in CW changes from a completely stirred tank reactor to a plug flow reactor (PFR). However, when affected by porosity, the flow approaches PFR in a larger mode implying that porosity influences the flow pattern in FWS CW. The average hydraulic efficiencies without any porosity effect are approximately 0.2. In a poorly designed FWS CW, increasing HLR does not actively modify hydraulic efficiency. Moreover, reducing the porosity from 100 to 76% increases the mean hydraulic efficiency to 0.54. Two empirical equations for the relationships of τm and the actual hydraulic efficiency with NR and the stem Reynolds number (NR∗) give CW investigators or designers to have a deeper understanding of the mean residence time and the hydraulic efficiency by RTD, NR, and NR∗.

Deciphering and modeling the physicochemical drivers of denitrification rates in bioreactors

Denitrification bioreactors have served as effective artificial N sinks by stimulating denitrification and remediating excessive nitrate. Predictions on bioreactor performance will be improved by quantifying the relationship between denitrification rates and causal factors which vary by geography (temperature), land-use intensity (NO3 concentration) and media type (carbon quality, quantity, and surface area). Experimental mesocosms filled with different wood media types (oak, pine), particle sizes and wood–sand volume ratios were exposed to flowing high-nitrate groundwater across a range of seasonal groundwater temperatures (8–24°C) to determine the influence of these coarse but utilitarian parameters on bioreactor performance. To increase the transferability and specificity of findings, a multivariate analysis was used to quantify relationships between denitrification rates, microbial biomass, temperature, media surface area to volume ratio and metrics of C quality to guide de novo media selection and performance predictions. There were no strong differences in hydraulic conductivity, media consumption rates, and TKN flux between different treatments although increasing the wood–sand volume ratio alone produced significant increases in denitrification rates and undesirable DOC leaching. Fluxes of DOC and TKN also increased with higher hydraulic loading rates. Denitrification rates were unresponsive to nitrate concentration and most strongly influenced by groundwater temperature (Q10=4.7), although carbon bioavailability and media surface area were uniquely predictive of denitrification rates. Bioreactor performance will therefore be most strongly influenced by geographical variations in temperature, although within a specific location, bioreactor media selection will influence denitrification rates.

Effect of artificial aeration on the performance of vertical-flow constructed wetland treating heavily polluted river water

AbstractThree lab-scale vertical-flow constructed wetlands (VFCWs), including the non-aerated (NA), intermittently aerated (IA) and continuously aerated (CA) ones, were operated at different hydraulic loading rates (HLRs) to evaluate the effect of artificial aeration on the treatment efficiency of heavily polluted river water. Results indicated that artificial aeration increased the dissolved oxygen (DO) concentrations in IA and CA, which significantly favored the removal of organic matter and NH4+-N. The DO grads caused by intermittent aeration formed aerobic and anoxic regions in IA and thus promoted the removal of total nitrogen (TN). Although the removal efficiencies of CODCr, NH4+-N and TN in the three VFCWs all decreased with an increase in HLR, artificial aeration enhanced the reactor resistance to the fluctuation of pollutant loadings. The maximal removal efficiencies of CODCr, NH4+-N and total phosphorus (TP) (i.e., 81%, 87% and 37%, respectively) were observed in CA at 19 cm/day HLR, while the maximal TN removal (i.e., 57%) was achieved in IA. Although the improvement of artificial aeration on TP removal was limited, this study has demonstrated the feasibility of applying artificial aeration to VFCWs treating polluted river water, particularly at a high HLR.

Enhanced nitrogen removal in a wastewater treatment process characterized by carbon source manipulation with biological adsorption and sludge hydrolysis

An innovative adsorption/nitrification/denitrification/sludge-hydrolysis wastewater treatment process (ENRS) characterized by carbon source manipulation with a biological adsorption unit and a sludge hydrolysis unit was developed to enhance nitrogen removal and reduce sludge production for municipal wastewater treatment. The system presented good performance in pollutants removal, yielding the effluent with average COD, NH4+-N, TN and TP of 48.5, 0.6, 13.2 and 1.0mg/L, respectively. Sixty percent of the total carbon source in the influent was concentrated and separated by the quick adsorption of activated sludge, providing the possibilities of reusing waste carbon source in the denitrification tank and accumulating nitrobacteria in the nitrification tank. Low temperature of 6–15°C and high hydraulic loading rate of 3.0–15.0m3/d did not affect NH4+-N removal performance, yielding the NH4+-N of lower 1.0mg/L in the effluent. Furthermore, 50% of the residual sludge in the ENRS system could be transformed into soluble COD (SCOD) by alkaline thermal hydrolysis with temperature of 60°C and pH of 11, and the hydrolyzed carbon could completely substitute methanol as a good quality carbon to support high efficient denitrification.

Study of a Novel Vertical Flow Constructed Wetland System with Drop Aeration for Rural Wastewater Treatment

Constructed wetlands are recognized as a reliable technology for rural wastewater treatment. However, conventional constructed wetlands face problems with low pollutant removal efficiency and limited oxygen transfer capability. Therefore, a novel vertical flow constructed wetland (VFCW) system with drop aeration was developed in this study. Two pilot-scale vertical flow constructed wetlands of 0.75 m2 each were constructed with the same dimensions and configuration but different media, one of which (named as CW1) was filled with a 1:1 mixture (by weight) of zeolite and dolomite and the other (named as CW2) with the same zeolite only. The oxygen transfer capability of a multilevel two-layer drop aeration device, organics and nitrogen removal of CW1 and CW2, and pollutant distribution along the depths of CW1 and CW2 in different operational phases were studied. The results demonstrated that compared with the direct drop aeration process, the multilevel, two-layer drop aeration device supplied 2–6 mg/L higher dissolved oxygen per meter of drop height, and after installation of the six-level, two-layer drop aeration devices, the 5-day biochemical oxygen demand removal load was improved from 8.1 to 14.2 g m−2 day−1 for CW1. With regard to the different filter media, nitrogen removal was improved by the adsorption of zeolite in the first year, with 5–36% higher NH 4 + –N removal efficiency of CW2 compared with that in CW1. Since it did not have a significant positive effect on phosphate removal, dolomite can be replaced by zeolite. The chemical oxygen demand removal mainly took place in the upper 15-cm filter layer in different operational phases, while nitrogen distribution along the depths of the VFCWs was different in different operational phases. In addition, as no operational problems occurred, the vertical flow constructed wetland system with drop aeration is an appropriate alternative for rural wastewater treatment, with numerous advantages of low capital and operation costs, no energy consumption, easy maintenance, high hydraulic loading rate, high pollutant removal efficiency, and no clogging.

Tapered anaerobic hybrid reactor – a better option for treating low‐strength wastewaters

Anaerobic biofilm reactors have limitations in treating wastewaters with low organic substrate concentrations (COD value below 1000 mg/L) because the substrate cannot reach the microorganisms present in the interior part of the biogranules. Hence, the performance of these reactors is mainly influenced by the size of the biogranules present within the reactor. An anaerobic hybrid reactor with a tapered configuration has been developed where the self‐immobilized biogranules are kept under completely fluidized condition. The tapered configuration can retain smaller sized biogranules more effectively than a cylindrical configuration for the same hydraulic loading rate. A synthetic effluent containing glucose as the sole carbon source was used to study the performance of this reactor. The reactor could handle an organic loading rate up to 19.1 kgCOD/(m3·d) with a hydraulic retention time (HRT) of 0.63 h, removing around 90% of inlet COD. Even though the strength of the wastewater is low, the resultant organic loading rate is also high because of the high hydraulic loading rate (low HRT). The specific substrate utilization rate study showed that the concentration of methanogenic bacteria within the biogranules increased along the reactor height, whereas the concentration of acidogens decreased. The morphology and hydrodynamic characteristics of the biogranules obtained from the reactor at different heights were also studied. The biogranules obtained from the upper port of the reactor had a lower diameter, lower terminal settling velocity and more cavities than those from the lower port. Biogranules up to the size of 5.2 mm were observed.

Effects of Natural Organic Matter on PCB‐Activated Carbon Sorption Kinetics: Implications for Sediment Capping Applications

In situ capping of polychlorinated biphenyl (PCB)-contaminated sediments with a layer of activated carbon has been proposed, but several questions remain regarding the long-term effectiveness of this remediation strategy. Here, we assess the degree to which kinetic limitations, size exclusion effects, and electrostatic repulsions impaired PCB sorption to activated carbon. Sorption of 11 PCB congeners with activated carbon was studied in fixed bed reactors with organic-free water (OFW) and Suwannee River natural organic matter (SR-NOM), made by reconstituting freeze-dried SR-NOM at a concentration of 10 mg L(-1) as carbon. In the OFW test, no PCBs were detected in the column effluent over the 390-d study, indicating that PCB-activated carbon equilibrium sorption capacities may be achieved before breakthrough even at the relatively high hydraulic loading rate (HLR) of 3.1 m h(-1). However, in the SR-NOM fixed-bed test, partial PCB breakthrough occurred over the entire 320-d test (HLRs of 3.1-, 1.5-, and 0.8 m h(-1)). Simulations from a modified pore and surface diffusion model indicated that external (film diffusion) mass transfer was the dominant rate-limiting step but that internal (pore diffusion) mass transfer limitations were also present. The external mass transfer limitation was likely caused by formation of PCB-NOM complexes that reduced PCB sorption through a combination of (i) increased film diffusion resistance; (ii) size exclusion effects; and (iii) electrostatic repulsive forces between the PCBs and the NOM-coated activated carbon. However, the seepage velocities in the SR-NOM fixed bed test were about 1000 times higher than would be expected in a sediment cap. Therefore, additional studies are needed to assess whether the mass transfer limitations described here would be likely to manifest themselves at the lower seepage velocities observed in practice.

Removal of nutrients from wastewater with Canna indica L. under different vertical-flow constructed wetland conditions

Constructed wetlands are becoming increasingly popular worldwide for removing contaminants from domestic wastewater. This study investigated the removal efficiency of nitrogen (N) and phosphorus (P) from wastewater with the simulated vertical-flow constructed wetlands (VFCWs) under three different substrates (i.e., BFAS or blast furnace artificial slag, CBAS or coal burn artificial slag, and MSAS or midsized sand artificial slag), hydraulic loading rates (i.e., 7, 14, and 21 cm d −1), and wetland operational periods (0.5, 1, and 2 years) as well as with and without planting Canna indica L. The wastewater was collected from the campus of South China Agricultural University, Guangzhou, China. Results show that the percent removal of total P (TP) and ammonium N (NH 4 +-N) by the substrates was BFAS > CBAS > MSAS due to the high contents of Ca and Al in substrate BFAS. In contrast, the percent removal of total N (TN) by the substrates was CBAS > MSAS > BFAS due to the complicated nitrification/denitrification processes. The percent removal of nutrients by all of the substrates was TP > NH 4 +-N > TN. About 10% more TN was removed from the wastewater after planting Canna indica L. A lower hydraulic loading rate or longer hydraulic retention time (HRT) resulted in a higher removal of TP, NH 4 +-N, and TN because of more contacts and interactions among nutrients, substrates, and roots under the longer HRT. Removal of NO 3 −N from the simulated VFCWs is a complex process. A high concentration of NO 3 −N in the effluent was observed under the high hydraulic loading rate because more NH 4 +-N and oxygen were available for nitrification and a shorter HRT was unfavorable for denitrification. In general, a longer operational period had a highest removal rate for nutrients in the VFCWs.

Characteristics of nutrient retention in a stormwater wetland during dry and wet days

A 0.23-ha pilot wetland was constructed to examine its effectiveness for the control of nonpoint source pollution (NPS) from a 7.42-ha agricultural watershed in Korea. The wetland was operated during base flow and storm flow conditions and monitored for four years (2006-2009). The wetland was operated under high hydraulic loading rates (HLRs, 0.78 m/day on average) during rainy days. The average influent nitrogen concentration was 9.8 mg/L during wet days, but around 11.6 mg/L during dry days. Due to the short hydraulic retention time (HRT) on wet days, nitrogen retention at the wetland was poor, only 6.1%; whereas, during dry days the efficiency was higher, around 17.9%. On rainy days, the wetland presented high retention for total phosphorus (TP), with an average efficiency of 68.3%, accompanied with a total suspended solids (TSS) removal of 84.7%. However, on dry days, the wetland showed positive soluble reactive phosphorus (SRP) retention other than TP. The interior of the wetland was observed to have different nutrients levels. Furthermore, suggestions are addressed in terms of improved design for better performance.

Aeration characteristics of a rectangular stepped cascade system

Aeration experiments, maintaining nappe flow conditions, were carried out on a rectangular stepped cascade of total height 3.0 m to determine the total number of steps, slope of the entire cascade and hydraulic loading rate at which maximum overall aeration efficiency occurs, keeping the surface area of individual steps constant. Based on dimensional analysis, the overall aeration efficiency at standard conditions (E(20)) was expressed as a function of square of total number of steps (N(2)) and dimensionless discharge (d(c)/h), where d(c) and h represent critical depth in a rectangular prismatic channel and individual step height respectively. An empirical equation with E(20) as the response and N(2) and d(c)/h as the independent parameters was developed based on the experimental results subject to 36<or=N(2)<or =196 and 0.009<or=d(c)/h< or=0.144. The experimental results showed that the overall aeration efficiency (E(20)) for a particular step height of stepped cascade increases with increase in d(c)/h up to a certain value and then decreases. This may be due to at higher d(c)/h, i.e., at higher hydraulic loading rate, the flow approaches the transition zone and thereby aeration efficiency decreases. E(20) was also found to increase with number of steps at any hydraulic loading rate, because of the increased surface area of fall. The optimum number of steps, slope of the entire stepped cascade and hydraulic loading rate were found to be 14, 0.351 and 0.009 m(2)/s respectively producing the maximum value of overall aeration efficiency of 0.90.

Attenuation of pollutants in sanitary sewer overflow: Comparative evaluation of treatment with fixed media bioreactors

Five types of fixed media bioreactors (biofilters) – sand, felt (textile), peat, felt/sand, and peat/sand – were used to treat sanitary sewer overflow (SSO). A simulated 6-h peak flow of a 25-yr SSO event contained 40–125 mg/l biochemical oxygen demand (BOD 5) and was loaded on the bioreactors at a high hydraulic loading rate of 0.2 m/h. The sand bioreactors were the most effective in the treatment, reducing BOD 5 by 84 ± 9%. The combination media peat/sand and felt/sand showed similar efficiency with peat, higher than felt. After the initial start-up, all the bioreactors reached >90% reduction of total suspended solids. The bioreactors also effectively removed ammonia and total phosphorus concentrations in a 2-h SSO loading, which would occur more often than a 6-h peak flow in a 25-yr SSO event. The effluent concentration of nutrients increased with continued loadings after the first 2 h.

Influence of design and operating conditions on the removal of MS2 bacteriophage by pilot-scale multistage slow sand filtration

Research Article| November 01 2009 Influence of design and operating conditions on the removal of MS2 bacteriophage by pilot-scale multistage slow sand filtration William B. Anderson; William B. Anderson 1Department of Civil & Environmental Engineering, University of Waterloo, Waterloo Ontario, Canada N2L 3G1 Tel.: 519-888-4567, ext. 33265 Fax: 519-746-7499; E-mail: wbanderson@uwaterloo.ca Search for other works by this author on: This Site PubMed Google Scholar Jeffrey L. DeLoyde; Jeffrey L. DeLoyde 2Stantec Consulting Engineers, 1505 Laperriere Avenue, Ottawa Ontario, Canada K1Z 7T1 Search for other works by this author on: This Site PubMed Google Scholar Michele I. Van Dyke; Michele I. Van Dyke 1Department of Civil & Environmental Engineering, University of Waterloo, Waterloo Ontario, Canada N2L 3G1 Search for other works by this author on: This Site PubMed Google Scholar Peter M. Huck Peter M. Huck 1Department of Civil & Environmental Engineering, University of Waterloo, Waterloo Ontario, Canada N2L 3G1 Search for other works by this author on: This Site PubMed Google Scholar Journal of Water Supply: Research and Technology-Aqua (2009) 58 (7): 450–462. https://doi.org/10.2166/aqua.2009.140 Article history Received: May 13 2009 Accepted: September 10 2009 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Cite Icon Cite Permissions Search Site Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsThis Journal Search Advanced Search Citation William B. Anderson, Jeffrey L. DeLoyde, Michele I. Van Dyke, Peter M. Huck; Influence of design and operating conditions on the removal of MS2 bacteriophage by pilot-scale multistage slow sand filtration. Journal of Water Supply: Research and Technology-Aqua 1 November 2009; 58 (7): 450–462. doi: https://doi.org/10.2166/aqua.2009.140 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex This paper summarizes findings from sixteen MS2 bacteriophage (MS2) challenge tests on biologically mature pilot-scale slow sand filters, conducted at varying water temperatures (<10° and >20°C), two hydraulic loading rates (0.1 vs. 0.4 m/h), and two bed depths (0.4 vs. 0.9 m). Few studies have quantified virus removal by slow sand filters at filtration rates on the high end and bed depths on the low end of typical practice, and none report virus removal below 5°C. The conditions investigated are important, because high filtration rates and low bed depths are sometimes seen as ways of making slow sand filtration more cost effective. MS2 removal increased with greater sand depth and warmer water temperature, but decreased at the higher hydraulic loading rate. Average MS2 removals ranged from 0.1 to 0.2 log in the roughing filters and 0.2 to 2.2 log in the slow sand filters. Shedding of MS2 was observed for up to 12 days after seeding was stopped. As a stand-alone process, slow sand filtration (with or without roughing filtration) may not provide adequate virus removal under some conditions and should be combined with a disinfection/inactivation step to provide robust compliance with regulatory requirements and protection of human health. drinking water, MS2 phage, slow sand filtration, virus This content is only available as a PDF. © IWA Publishing 2009 You do not currently have access to this content.

Nitrification‐Denitrification Biological Treatment of a High‐Nitrogen Waste Stream for Water‐Reuse Applications

This research was conducted to evaluate the use of biological nitrification-denitrification systems as pre-processors for recycling wastewater to potable water in support of space exploration. A packed-bed bioreactor and membrane-aerated nitrification reactor were operated in series with a 10:1 recycle ratio over varying loading rates. The dissolved organic carbon (DOC) removal exceeded 80% for all loading rates (theta = 1 to 6.8 days), while total nitrogen removal generally increased with decreasing retention time, with a maximum removal of 55%. The degree of nitrification generally declined with decreasing retention time from a high of 80% to a low of 60%. Maximum DOC and total nitrogen volumetric removal rates exceeded 1000 and 800 g/m3 x d, respectively, and maximum nitrification volumetric conversion rates exceeded 300 g/m3 x d. At low hydraulic loading rates, the system was stoichiometrically limited, while kinetic limitations dominated at high hydraulic loading rates. Incomplete nitrification occurred at high loading rates, likely as a result of the high pH and large concentrations of ammonia.

Measurement of bubble bed depth in dissolved air flotation using a particle counter

In the development of dissolved air flotation (DAF) technology, it is noteworthy that higher hydraulic loading rates are achieved while the reactors become deeper resulting in a smaller footprint. One of the reasons for the increased efficiency is claimed to be the deeper bubble bed depth in the flotation separation zone; however, there has been limited research on the characterization of the bubble bed. In this research, a method for locating the bubble bed interface using a commercially available particle counter is presented. The results compared remarkably well with observations by the naked eye at a pilot plant with a transparent acrylic wall. The method is then applied to locate the bubble bed interface at an operating DAF plant in Wonju, Korea. We can observe that the bubble bed profile changes according to the operational conditions and that higher effluent water quality is obtained with a deeper bubble bed. Based on these results, optimization of DAF process might be possible by monitoring the bubble bed profile in the reactor.

Pilot-scale comparison of constructed wetlands operated under high hydraulic loading rates and attached biofilm reactors for domestic wastewater treatment

Four different pilot-scale treatment units were constructed to compare the feasibility of treating domestic wastewater in the City of Heraklio, Crete, Greece: (a) a free water surface (FWS) wetland system, (b) a horizontal subsurface flow (HSF) wetland system, (c) a rotating biological contactor (RBC), and (d) a packed bed filter (PBF). All units operated in parallel at various hydraulic loading rates (HLR) ranging from 50% to 175% of designed operating HLR. The study was conducted during an 8 month period and showed that COD removal efficiency of HSF was comparable (> 75%) to that of RBC and PBF, whereas that of the FWS system was only 57%. Average nutrient removal efficiencies for FWS, HSF, RBC and PBF were 6%, 21%, 40% and 43%, respectively for total nitrogen and 21%, 39%, 41% and 42%, respectively for total phosphorus. Removals of total coliforms were lowest in FWS and PBF (1.3 log units) and higher in HSF and RBC (2.3 to 2.6 log units). HSF showed slightly lower but comparable effluent quality to that of RBC and PBF systems, but the construction cost and energy requirements for this system are significantly lower. Overall the final decision for the best non-conventional wastewater treatment system depends on the construction and operation cost, the area demand and the required quality of effluent.

Field Evaluation of the Performance of Engineered On-Site Wastewater Treatment Units

A conventional on-site wastewater system (OWS) is traditionally comprised of one or more septic tanks for treatment of raw wastewater followed by percolation through natural soil to achieve purification prior to groundwater recharge. Other types of engineered treatment units (e.g., sand filters, textile media filters) may be implemented where site conditions are not suitable for conventional systems or in sensitive areas, such as those with nitrogen loading concerns. The research presented here is part of a large field study conducted to evaluate the purification performance of OWS employing three different engineered treatment units: a septic tank, a septic tank with a textile filter unit (TFU), and a septic tank with a membrane bioreactor (MBR). The TFU or MBR employ treatment processes that are designed to achieve higher purification compared to a septic tank so that soil treatment can be accomplished at higher hydraulic loading rates and/or with less unsaturated soil depth. This paper describes the in...