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This paper characterizes the composition of extracellular polymeric substances (EPSs) in different types of activated sludge (AS) processes and analyzes the biosorption of soluble organics when waste AS (WAS) is mixed with raw wastewater for primary carbon diversion. The fraction of AS organics identified as EPSs was 26% in a membrane bioreactor (MBR), 54% in conventional AS (CAS), and 51% in a trickling filter/solids contact (TF/SC) process. EPSs were found to be approximately 15% carbohydrates, 40% proteins, 40% humics, and 5% uronics in CAS and MBR AS. Biosorption was not correlated to the organic portion (VSS) of the WAS; however, statistically significant correlations were found for the total amount of EPSs (for TF/SC and CAS) and the protein fraction (for TF/SC and MBR) in the VSS. EPSs from different types of AS biosorbed the same amount of soluble organics, removing 1.43 ± 0.15 (n = 16) mg of soluble chemical oxygen demand (sCOD), and 1.20 ± 0.18 (n = 16) mg of truly soluble COD (ffCOD), per mg of cation exchange resin (CER) total extracted EPSs. Utilizing multiple extraction methods in series (CER–base–sulfide) increased EPS extraction yields by nearly 100% relative to CER alone and indicated different EPS fractionization for CAS (a smaller fraction of carbohydrates and a larger fraction of humics). [ABSTRACT FROM AUTHOR]

Green roofs can mitigate urban rooftop stormwater runoff. However, the lack of accurate, physically-based performance assessment and design models has hindered their wide application. Most hydrologic or hydraulic models have no direct connection to the physical properties of green roof components such as media type/depth, drainage depth, etc. In an effort to assist design engineers, a simplified yet effective physically-based model was developed and calibrated with pilot data in order to provide green roof hydrologic performance curves to guide design. Precipitations with depths ranging from 0 to 40 cm and durations 30 to 1440 min were simulated for 21 green roof designs to determine the effects of common physical design parameters. Results revealed that effective capacity and transient capacity are the controlling factors for runoff volume reduction for single precipitation events. Including a water storage feature in the design increased cumulative long-term runoff reduction by an average of 23.5%, whereas increasing growth media depth yielded an average 5.3% improvement. Peak reduction and peak delay are governed by media depth and drainage opening size. Study results indicate that LEED criteria should be modified to require specific designer-controlled parameters of storage and media depth for the design storm to ensure desired performance. [ABSTRACT FROM AUTHOR]

This paper conducts a comparative assessment of the environmental impacts of three methods of treating primary clarifier effluent in wastewater treatment plants (WWTPs) through life cycle assessment methodology. The three technologies, activated sludge (AS), high rate anaerobic-aerobic digestion (HRAAD), and trickling filter (TF), were assessed for treatment of wastewater possessing average values of biochemical oxygen demand and total suspended solids of 90 mg L-1 and 70mg L-1, respectively. The operational requirements to process the municipal wastewater to effluent that meets USEPA regulations have been calculated. The data for the AS system were collected from the East Honolulu WWTP (Hawaii, USA) while data for the HRAAD system were collected from a demonstrationscale system at the same plant. The data for the TF system were estimated from published literature. Two different assessment methods have been used in this study: IMPACT 2002þ and TRACI 2. The results show that TF had the smallest environmental impacts and that AS had the largest, while HRAAD was in between the two but with much reduced impacts compared with AS. Additionally, the study shows that lower sludge production is the greatest advantage of HRAAD for reducing environmental impacts compared with AS. [ABSTRACT FROM AUTHOR]

A green roof is an environmentally friendly best management practice for volume reduction, peak flow reduction, and peak delay of stormwater runoff from impervious rooftops. In this study, HYDRUS-2D was used to model the hydrologic response of a pilot green roof system. The root-mean-square deviation (RMSD) of growth media volumetric water content values between model and field measurements ranged between 0.38 and 1.74%. A method was developed to use the water content profile at three media depths to derive regression equations that predict hydrologic performance. These equations show that runoff volume reduction follows an inverse relationship between media field capacity and precipitation depth, that peak flow reduction obeys a second-order equation between media field capacity and precipitation depth, and that peak delay time can be approximated by a third-order equation that includes maximum capacity and precipitation depth. The R2s values of the regressions range between 0.87 and 0.99. These derived equations can be used for performance evaluations or design work, including determining the necessary green roof media depth to meet Leadership in Energy and Environmental Design (LEED) runoff reduction requirements. [ABSTRACT FROM AUTHOR]

Coastal Zone Act Reauthorization Amendments (CZARA, Section 6217) necessitate the requirement that onsite wastewater disposal units located near impaired surface waters or groundwater to provide at least 50% nitrogen removal. Approximately 38% of Hawaii households use onsite systems including septic tanks and cesspools that cannot meet this requirement. Upgrades to aerobic treatment units (ATUs) are a possible compliance solution. In Hawaii, ATUs must meet National Sanitation Foundation Standard 40 (NSF40) Class I effluent criteria. Previously, a multi-chamber, flowthrough, combined attached/suspended growth type ATU (OESIS-750) and presently, a sequencing batch type ATU (CBT 0.8KF-210) were evaluated for NSF40 compliance, nutrient removal capability (NSF245), and adaptability for water reuse (NSF350). Both units easily achieved the NSF40 Class I effluent criteria. While the OESIS-750 achieved only 19% nitrogen removal, the CBT unit achieved 81% nitrogen removal, meeting the NSF245 criteria and CZARA requirements for applications in critical wastewater disposal areas. In addition, the CBT consistently produced effluent with turbidity less than 2 NTU (NSF350) and UVT254 greater than 70%, facilitating the production of unrestricted-use recycled water. [ABSTRACT FROM AUTHOR]

Onsite sewage disposal systems (OSDSs) are the third leading cause of groundwater contamination in the USA. The existing condition of OSDSs in the State of Hawaii was investigated to determine whether a mandatory management program should be implemented. Based on observed conditions, OSDSs were differentiated into four categories: 'pass', 'sludge scum', 'potential failure' and 'fail'. Of all OSDSs inspected, approximately 68% appear to be in good working condition while the remaining 32% are failing or are in danger of failing. Homeowner interviews found that 80% of OSDSs were not being serviced in any way. About 70% of effluent samples had values of total-N and total-P greater than typical values and 40% had total suspended solids (TSS) and 5-day biochemical oxygen demand (BOD5) greater than typical values. The performance of aerobic treatment units (ATUs) was no better than septic tanks and cesspools indicating that the State's approach of requiring but not enforcing maintenance contracts for ATUs is not working. In addition, effluent samples from OSDSs located in drinking water wells estimated 2-year capture zones had higher average concentrations of TSS, BOD5, and total-P than units outside of these zones, indicating the potential for contamination. These findings suggest the need to introduce a proactive, life-cycle OSDS management program in the State of Hawaii. [ABSTRACT FROM AUTHOR]

Green roofs reduce runoff from impervious surfaces in urban development. This paper reviews the technical literature on green roof hydrology. Laboratory experiments and field measurements have shown that green roofs can reduce stormwater runoff volume by 30 to 86%, reduce peak flow rate by 22 to 93% and delay the peak flow by 0 to 30 min and thereby decrease pollution, flooding and erosion during precipitation events. However, the effectiveness can vary substantially due to design characteristics making performance predictions difficult. Evaluation of the most recently published study findings indicates that the major factors affecting green roof hydrology are precipitation volume, precipitation dynamics, antecedent conditions, growth medium, plant species, and roof slope. This paper also evaluates the computer models commonly used to simulate hydrologic processes for green roofs, including stormwater management model, soil water atmosphere and plant, SWMS-2D, HYDRUS, and other models that are shown to be effective for predicting precipitation response and economic benefits. The review findings indicate that green roofs are effective for reduction of runoff volume and peak flow, and delay of peak flow, however, no tool or model is available to predict expected performance for any given anticipated system based on design parameters that directly affect green roof hydrology. [ABSTRACT FROM AUTHOR]

An enricher-reactor process in which acclimated biomass is grown in an offline reactor on high concentrations of enrichment substrates was used to bioaugment a conventional activated sludge process to a toxic compound, 1-amino naphthalene. Various levels of bioaugmentation, ranging from I to 16% mass ratio of augmented cells to indigenous cells, were evaluated in laboratory-scale reactors. The experimental results showed that bioaugmentation can enhance toxic compound removal, increase resistance to shock loading, and reduce the time required for acclimation to the toxic compound. A process model was developed and calibrated using the experimental data. This model was then used to compare the process to an in-situ bioaugmentation process using a reaeration reactor that receives a portion of the recycle activated sludge. The model predicted experimentally observed removals of toxic compound and decreasing relative benefits of bioaugmentatiori at higher levels. The model suggests that augmented biomass suffers higher decay, which likely is due to the effects of its removal from a substrate-rich to substrate-poor environment. The model shows that the enricher-reactor-process has advantages at lower mean cell retention time (MCRT), and the in-situ process is superior at higher MCRT. Both processes can remove the toxic compound when operating below the washout MCRT that would occur in an unaugmented activated sludge process. [ABSTRACT FROM AUTHOR]

Ozone mass transfer in reclaimed water was evaluated at pilot scale to determine mass-transfer characteristics and reaction kinetics and to assess the use of oxygen as a surrogate to measure this process. Tests were conducted in a 40-L/min pilot plant over a 3-year period. Nonsteady-state mass-transfer analyses for both oxygen and ozone were performed for superficial gas flow rates ranging from 0.13m/min to 0.40m/min. The psi factor, which is the ratio of volumetric mass-transfer coefficients of ozone to oxygen, was determined. The decrease in oxygen transfer rate caused by contaminants in reclaimed water was only 10 to 15% compared to tap water. A simple mathematical model was developed to describe transfer rate and steady state ozone concentration. Ozone decay was modeled accurately as a pseudo first-order reaction between ozone and ozone-demanding materials. [ABSTRACT FROM AUTHOR]

Approximately one-quarter of housing units in the United States are not connected to centralized, publicly owned wastewater treatment works and instead operate their own cesspools or septic tanks that provide only partial treatment. A study was conducted in which a commercially available, on-site, residential wastewater package unit was tested at its design capacity according to an established protocol to determine if it could produce a high-quality effluent. Additional pilot-scale sand filtration and ultraviolet disinfection units were fabricated and operated to determine the feasibility of producing recycled water suitable for residential reuse and which could meet strict water reuse regulations. The results indicate that the package unit can produce an effluent equivalent to secondary effluent when properly operated and maintained. In addition, using add-on sand filter and ultraviolet light disinfection units, it was possible to produce the highest quality of reclaimed water recognized by Hawaii regulations (oxidized, filtered, disinfected, unrestricted use). It was also possible and may be economically feasible to produce a slightly lower quality reclaimed water (oxidized, disinfected, R-2) suitable for residential subsurface irrigation. [ABSTRACT FROM AUTHOR]

Extracellular polymeric substances (EPS) reportedly make up approximately half of the organic matter in activated sludge (AS), and therefore strongly influence AS properties. This study evaluated the component fractions of EPS normalized to volatile suspended solids (VSS) in waste activated sludge (WAS) from a trickling-filter-solids contact process (TF/SC) and its ability to biosorb organic matter from raw wastewater with 30 min of contact time. Biosorption is the process in which organic matter (carbohydrates, proteins, humic acids, DNA, uronic acids, and lipids) in a sorbate, such as raw wastewater, sorbs onto a sorbent such as WAS. A statistically significant correlation was found between both the total concentration of EPS and the proteins component of the EPS and the biosorption removal of soluble chemical oxygen demand (sCOD) and truly soluble COD (ffCOD). Thus, the biosorption of soluble forms of COD can accurately be predicted by quantifying just the amount of proteins in WAS-associated EPS. No significant correlations were found for the biosorption of colloidal COD (cCOD). WAS biosorbed 45–75 mg L−1 of COD in 30 min. WAS absorbed or stored the proteins fraction of the soluble microbial products (SMP) during the biosorption process. Higher concentrations of humic acids were found in the biosorption process effluent than in the untreated wastewater, which warrants further study. Longer cation exchange resin (CER) extraction times yielded more total EPS from the sludge: 90 ± 9, 158 ± 3, and 316 ± 44 mg g−1 VSS, for 45-min, 4-h, and 24-h extraction times, respectively. Thus, EPS extracted represented only 9%, 15.8%, and 31.6% of the VSS, respectively, raising questions about whether the accurate characterization of EPS can be performed using the typical extraction time of 45 min due to different extraction rates for different components. It was found that the humic acids fraction was extracted much more slowly than the other fractions. [ABSTRACT FROM AUTHOR]