High rate biological contactor system using waste activated sludge from trickling filter/solids contact process.

A high-rate biological contactor process (HRBC) can be used as primary treatment instead of a clarifier to remove particulate, colloidal and soluble fractions of organic matter via biosorption plus flotation and divert it to anaerobic digestion for methane production, simultaneously reducing secondary aeration energy demand. Pilot and bench tests were conducted at a range of contact times (15-60 min) and contactor dissolved oxygen (DO) (0.2-2.0 mg/L) using waste activated sludge (WAS) from a trickling filter/solids contact (TF/SC) process in the HRBC. Biosorption performance was lowest when contact times were <30 min and unstable at DO < 0.5 mg/L. The overall average of 20% sCOD capture was similar to previous findings by others using WAS from conventional AS. The biomethane potential (BMP) of the HRBC float material can be as high as that of primary sludge (340-400 mL CH4/g VS), which is much greater than WAS. Operating the HRBC with a long contact time (>30 min) or with high DO (>1 mg/L) increases the amount of biosorption but reduces the BMP of the float. It was also found that biosorption only effectively occurs when a WAS is paired with the wastewater from the same facility.

Anaerobic-aerobic biofilm-based digestion of chemical contaminants of emerging concern (CEC) and pathogen indicator organisms in synthetic wastewater.

The efficacy of biofilm based anaerobic-aerobic treatment to reduce caffeine, carbamazepine, and three estrogens (Estrone (E1), 17ß-estradiol (E2), and 17α-ethynylestradiol (EE2)), as well as E. coli (CN-13) and F+ specific coliphage (MS2), from synthetic wastewater was investigated. Results showed no observable reduction of carbamazepine by either anaerobic or aerobic biofilms over a dosing period of 51-days followed by an additional 23 days of observation. Caffeine, by contrast, was reduced by 11.09% in the upflow anaerobic packed bed biofilm reactor (UAnPBBR) and by 91.90% in the aerobic trickling filter biofilm reactor (TF). Estrone (E1) and 17ß-estradiol (E2) showed minimal reduction in the UAnPBBR but 99.67% reduction in the TF, while EE2 was reduced 1.62% in the AnPBBR and 20.36% in the TF. On average, a 3-log reduction of E. coli (CN-13) and a 1-log reduction of F+ specific coliphage (MS2) concentration was observed across the overall reactor system.

Adsorption of 1,2,3-Trichloropropane (TCP) to meet a MCL of 5 ppt.

1,2,3-Trichloropropane (TCP) is a groundwater contaminant in the drinking water aquifers in Hawaii and some other states. Granular activated carbon (GAC) has been used for 30 years to treat approximately 60 million gallons per day of TCP-contaminated groundwater in Hawaii. The State of Hawaii's current maximum contaminant level (MCL) for TCP is 600 ng/L (ppt), and consideration is being given to lower the MCL to 5 ppt. There is no EPA MCL for TCP. A study was conducted to determine if any GAC could meet a 5 ppt MCL for TCP, and if so, how many bedvolumes (BVs) could be treated prior to breakthrough. Constant Diffusivity-Rapid Small-Scale Column Tests (CD-RSSCTs) were performed to evaluate GAC adsorption of TCP. Three different groundwaters and six different GACs were utilized. The RSSCTs with the currently-utilized GAC were predictive of the performance of the GAC contactors (50,000 BVs to breakthrough). Any of the six GACs could meet a MCL of 5 ppt and some could do so for 150,000 or more BVs. No single GAC was optimal for all three well sites, indicating effects of subtle undefined differences in the water matrix and/or GAC physiochemical properties. The coal-based direct-activated carbon currently being used is the least optimal for all three well sites with respect to meeting a potential new TCP MCL of 5 ppt. The most effective GACs for Kunia were the Calgon coal-based GAC and the Siemens enhanced coconut shell GAC, while the most effective for Waipahu were the Siemens regular and enhanced coconut shell GACs, and the most effective for Mililani was the Calgon coal-based GAC. Choosing just one GAC for use at all three well sites (rather than the optimal for each site) would result in a reduction of treatment run time of 1 year at one well site (63% reduction).

Life cycle assessment comparison of activated sludge, trickling filter, and high-rate anaerobic-aerobic digestion (HRAAD).

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 70 mg 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 demonstration-scale 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 2002+ 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.

Enhanced nitrogen removal with an onsite aerobic cyclic biological treatment unit.

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, flow-through, 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.

Condition assessment survey of onsite sewage disposal systems (OSDSs) in Hawaii.

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.

Green roof hydrologic performance and modeling: a review.

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.

Pilot-scale in situ bioremediation of HMX and RDX in soil pore water in Hawaii.

A nine-month in situ bioremediation study was conducted in Makua Military Reservation (MMR) in Oahu, Hawaii (USA) to evaluate the potential of molasses to enhance biodegradation of royal demolition explosive (RDX) and high-melting explosive (HMX) contaminated soil below the root zone. MMR has been in operation since the 1940's resulting in subsurface contamination that in some locations exceeds USEPA preliminary remediation goals for these chemicals. A molasses-water mixture (1 : 40 dilution) was applied to a treatment plot and clean water was applied to a control plot via seven flood irrigation events. Pore water samples were collected from 12 lysimeters installed at different depths in 3 boreholes in each test plot. The difference in mean concentrations of RDX in pore water samples from the two test plots was very highly significant (p < 0.001). The concentrations differences with depth were also very highly significant (p < 0.001) and degradation was greatly enhanced at depths from 5 to 13.5 ft. biodegradation was modeled as first order and the rate constant was 0.063 per day at 5 ft and decreased to 0.023 per day at 11 ft to 13.5 ft depth. Enhanced biodegradation of HMX was also observed in molasses treated plot samples but only at a depth of 5 ft. The difference in mean TOC concentration (surrogate for molasses) was highly significant with depth (p = 0.003) and very highly significant with treatment (p < 0.001). Mean total nitrogen concentrations also differed significantly with treatment (p < 0.001) and depth (p = 0.059). The molasses water mixture had a similar infiltration rate to that of plain water (average 4.12 ft per day) and reached the deepest sensor (31 ft) within 5 days of application. Most of the molasses was consumed by soil microorganisms by about 13.5 feet below ground surface and treatment of deeper depths may require greater molasses concentrations and/or more frequent flood irrigation. Use of the bioremediation method described herein could allow the sustainable use of live fire training ranges by enhancing biodegradation of explosives in situ and preventing them from migrating to through the vadose zone to underlying ground water and off-site.

Survey of attitudes and perceptions of urine-diverting toilets and human waste recycling in Hawaii.

Urine constitutes only about 1% of domestic sewage but contains 50% or more of the excreted nutrients and chemicals like hormones and pharmaceutical residues. Urine diverting toilet (UDT) systems can be considered a more sustainable alternative to wastewater management because they allow nutrient recycling, reduce water use, and allow source-separation of hormones and chemicals that can harm the environment. An online survey was conducted to determine whether UDTs are acceptable to the general public in Hawaii and if attitudes and perceptions towards it and human waste (HW) recycling vary with age, sex, level of education, religious affiliation, ethnicity, and employment status. The survey was also intended to detect possible drivers and barriers for the UDTs. Variations on variables were tested at 5% significance (p=0.05) level (Chi-squared test or ANOVA) and considered significantly different if the p-value was less than 0.05. The results were encouraging as more than 60% are willing to pay extra for the UDT, while only 22% knew that such systems existed. No statistically significant difference was found between males and females on all survey questions at the 5% level. However, females had higher willingness to pay (WTP) than males and WTP increased with age and income. The WTP of Caucasians was higher than Asians and differed significantly. Some respondents expressed concern about the legal provisions for recycling of HW. The survey results indicate that with a public education program, it is possible that most people would be willing to adopt UDTs and HW recycling with incurred societal benefits of reduced water and fertilizer use, reduced greenhouse gas emissions, and collection of micropollutants at the source to prevent their entry into waterways. Because of the small sample size (N=132, 13% response rate) the survey is not representative but may be indicative of the general attitude of Hawaiian people.

Molasses enhanced phyto and bioremediation treatability study of explosives contaminated Hawaiian soils.

A 15-week treatability study was conducted in a greenhouse to evaluate the potential effects of molasses on the bioremediation and phytoremediation potential of Guinea Grass (Panicum maximum) for treating energetic contaminated soil from the open burn/open detonation area of the Makua Military Reservation, Oahu, HI (USA). The energetics in the soil were royal demolition explosive (RDX) and high-melting explosive (HMX). Among the 6 treatments employed in this study, enhanced removal of RDX was observed from treatments that received molasses and went to completion. The RDX degradation rates in treatments with molasses diluted 1:20 and 1:40 were comparable suggesting that the lower dose worked as well as the higher dose. Treatments without molasses degraded RDX slowly and residuals remained after 15 weeks. The bacterial densities in molasses-treated units were much greater than those without molasses. Phytoremediation alone seems to have little effect on RDX disappearance. For HMX, neither bioremediation nor phytoremediation was found to be useful in reducing the concentration within the experimental period. The concentrations of nitrogen and phosphorous in the soil did not change significantly during the experiment, however, a slight increase in soil pH was observed in all treatments. The study showed that irrigating with diluted molasses is effective at enhancing RDX degradation mainly in the root zone and just below it. The long term sustainability of active training ranges can be enhanced by bioremediation using molasses treatments to prevent RDX deposited by on-going operations from migrating through the soil to groundwater and off-site.

Modeling the performance of hazardous wastes removal in bioaugmented activated sludge processes.

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 1 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 bioaugmentation 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.

Modeling ozone mass transfer in reclaimed wastewater.

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.

Determination of biodegradable dissolved organic carbon using entrapped mixed microbial cells.

Several methods for determining biodegradable dissolved organic carbon (BDOC) in water have been developed within the last two decades. However, the problem with most of these methods is the length of time required for the start-up (colonization) and/or determination from days to weeks. In this study, a simple and rapid continuous bioreactor procedure using immobilized cells was developed for BDOC determination. In the first stage of the development, the bioreactors were aerated to ensure that dissolved oxygen was not rate limiting. However, BDOC results obtained from the aerated bioreactors suffered from a large error caused by the release of background dissolved organic carbon (DOC). As a consequence, a different bioreactor scheme, in which the feed (sample) instead of the bioreactor was aerated, was tested. Results show that the feed aerated (FA) bioreactor is a better tool for BDOC determination especially for waters with low initial organic concentrations because of less background DOC released by the immobilized cell systems. Using the FA bioreactor, the accurate and reproducible measurement of BDOC can be achieved within a hydraulic retention time of 3 h, and no start-up period is required.