Michael K. Stenstrom

Sediment characteristics, phosphorus types and phosphorus release rates between river and lake sediments

The Han river is 469.7 km long with 26219-km2 area watershed, and is the primary drinking water source for the 20 million people that live in Seoul, Kangwon-Do and Kyunggi-Do, Korea. Phosphorus release from sediments impacts water quality, and is endangering the beneficial use of the river. This research measures phosphorus release and predicts future releases from bottom sediments of two tributary areas (Chungpyung Lake (CPL) and Jamsil submerged dam (JSD) area in the Han river). Sediment samples were taken over a 4-year period from four points in the Jamsil dam area and from 92 points in CPL. The sediments were analyzed for total phosphorus, the form of the phosphorus and release rates under different conditions to the water column. Sediment phosphorus distribution from CPL was 3-5% adsorbed-P (Ads-P), 15-20% non-apatite-P (NAI-P), 25-30% apatite-P (A-P) and 45-57% residual-P (R-P). In the JSD area, the phosphorus distribution ranges were 1-3% Ads-P, 22-39% NAI-P, 26-40% A-P and 30-39% R-P. Laboratory experiments showed that phosphorus release rates from 60 to 80 mg/m2 week in JSD area and ranged from 25 to 40 mg/m2 week in CPL sediments.

The effect of dissolved oxygen concentration on nitrification

The effect of dissolved oxygen concentration on the rate of nitrification has been investigated by a number of researchers using both pure and mixed cultures, and cultures found in wastewater treatment systems. The maximum growth rate of both nitrification reactions are reported to be affected by dissolved oxygen concentration over the range of 0.3 mg l−1 to as much as 4.0 mg l−1. In some instances, it has been reported that a dissolved oxygen concentration in excess of 4.0 mg l−1 is required to achieve maximum nitrification rates, while other investigators have found that only 0.5 to 1.0 mg l−1 is required. It has been proposed that several factors are responsible for the wide range of reported nitrification rates with varying dissolved oxygen concentrations. Among these factors are the effects of oxygen diffusion in flocs, variation between measured results due to steady-state and dynamic measuring techniques, and double-substrate limited kinetics. This paper reviews the nitrification literature with respect to the effects of dissolved oxygen concentration, and shows that double-substrate limiting kinetics could account for the variation in the reported results.

Effects of alpha, beta and theta factor upon the design, specification and operation of aeration systems

Aeration is an essential part of almost all wastewater treatment systems and is usually the major energyconsuming process. With the increasing cost of energy, there has been a resurgence of interest in aeration system design, specification, and operation. This increased interest is evidenced through a number of recent papers discussing general procedures and methods for aerations system evaluation, parameter estimation, and testing . A second factor which has created renewed interest in aeration systems is the lack of uniform, standardized testing and specification procedures. The U.S . Environmental Protection Agency and the American Society of Civil Engineers have jointly sponsored the development of a manual of practice for aerator testing and specification. A committee of interested manufacturers, consultants, aeration system users, and academics was set up to determine state-ofthe-art methods, and to define areas for future research and development. The committee has worked for approximately three years to ascertain state-of-the-art methods and has produced reports describing aspects of aeration system design, specification and testing. It is the purpose of this review paper to describe the findings of the subcommittee on alpha, beta, and theta factors. No discussion of general procedures will be made, and the reader is directed to recent general reviews and discussions of testing procedures by Bingel (1979), Boon (1980), Boyle (1979), Kayser (1979), Sweeris (1979), and Wheatland & Boon (1979), among others . Undoubtedly, other reports and papers will describe the committees findings with respect to other areas. It is hoped that this paper will provide a summary and review of all the relevant literature regarding alpha, beta, and theta factors.

First flush in a combined sewer system

Pollutant first flush was examined in an urban catchment with area of 12.7 ha and drained by a combined sewer system located in northern Italy. A total of 23 rainfall-runoff events were monitored and 281 samples were analyzed. The selected quality parameters were biochemical oxygen demand, chemical oxygen demand, suspended solids, settleable solids, total phosphorus, total nitrogen, ammonium nitrogen, lead, and zinc, specific conductivity and hydrocarbons. A subset of representative storms was selected for first flush analysis. The catchment presented a strong first flush for almost all storms and most constituents. The analysis shows that treating the maximum amount of the early part of the runoff is a better strategy than treating a constant flow rate. Best management practices that can treat or store the first runoff are favored in this kind of system for these water quality parameters.

Characteristics of highway stormwater runoff in Los Angeles: metals and polycyclic aromatic hydrocarbons.

Stormwater runoff from three highway sites in Los Angeles, California, was monitored, during the 2000 to 2003 wet seasons. Correlations among heavy metals, polycyclic aromatic hydrocarbons (PAHs), and storm characteristics were performed using datasets collected for 62 storm events. Statistical correlation analyses of the event mean concentrations (EMCs) and mass first-flush ratios (MFFs) with storm characteristics were conducted to determine if the first flush is related to site or storm characteristics. This study agreed with other highway runoff characterization studies, in that strong correlations were observed among the heavy metals and between heavy metals and total PAHs, and total suspended solids were well correlated with most heavy metals. Only antecedent dry days among storm characteristics were reasonably well-correlated with the EMCs of heavy metals and total PAHs, and dissolved and total metals exhibited similar MFFs, with approximately 30 to 35% of the mass being discharged in the first 20% of the runoff volume.

Appropriate wastewater treatment systems for developing countries: criteria and indictor assessment in Thailand

This paper presents a comprehensive approach with factors to select appropriate wastewater treatment systems in developing countries in general and Thailand in particular. Instead of focusing merely on the technical dimensions, the study integrates the social, economic, and environmental concerns to develop a set of criteria and indicators (C&I) useful for evaluating appropriate system alternatives. The paper identifies seven elements crucial for technical selection: reliability, simplicity, efficiency, land requirement, affordability, social acceptability, and sustainability. Variables are organized into three hierarchical elements, namely: principles, criteria, and indicators. The study utilizes a mail survey to obtain information from Thai experts-academicians, practitioners, and government officials-to evaluate the C&I list. Responses were received from 33 experts on two multi-criteria analysis inquiries-ranking and rating-to obtain evaluative judgments. Results show that reliability, affordability, and efficiency are among the most important elements, followed by sustainability and social acceptability. Land requirement and simplicity are low in priority with relatively inferior weighting. A number of criteria are then developed to match the contextual environment of each particular condition. A total of 14 criteria are identified which comprised 64 indicators. Unimportant criteria and indicators are discarded after careful consideration, since some of the indicators are local or site specific.

Biodegradable dissolved organic carbon for indicating wastewater reclamation plant performance and treated wastewater quality

Various methods for measuring biodegradable dissolved organic carbon (BDOC) in water have been introduced in the last decade. Applications of the methods have been limited to drinking water. The measure of BDOC has been used mainly to indicate the quality of raw and finished waters and evaluate the performance of biological activated carbon (ozone/granular activated carbon) systems in water treatment plants. Recently, a modified BDOC protocol was developed for examining reclaimed and secondary-treated wastewaters. Use of the new BDOC method can be extended to the wastewater treatment and reclamation fields. Samples collected from a wastewater reuse pilot facility were tested for BDOC, The modified BDOC method was able to detect the increase in biodegradability of ozonated tertiary-treated wastewater. Good relationships among BDOC, dissolved organic carbon (DOC), and soluble biochemical oxygen demand were obtained. The modified protocol was later used to measure BDOC in secondary-effluent samples from 13 municipal wastewater treatment plants. The results show that BDOC can also be used as an indicator of secondary-effluent quality. Likewise, strong and significant correlations were found among BDOC, DOC, and soluble chemical oxygen demand in secondary effluents.

Real-time aeration efficiency monitoring in the activated sludge process and methods to reduce energy consumption and operating costs.

Aeration is the most energy intensive unit operation in municipal wastewater treatment, and fine-pore diffusers have been widely used to minimize power consumption. Unfortunately, fine-pore diffusers suffer from fouling and scaling problems, which cause a rapid decline in aeration performance and significant increase in power consumption. Diffusers must be cleaned periodically to reduce energy costs. The cleaning frequency of diffusers is site-specific and its effectiveness can be evaluated with oxygen transfer efficiency (OTE) testing. Off-gas testing is the best technique for measuring OTE in real-time. Fine-pore diffusers have low a factors that are further reduced at high loading rate. A time-series of off-gas measurements were conducted to demonstrate the value of real-time OTE data for developing energy-conserving operating strategies. The observations confirm the inverse correlation between OTE and airflow rate as well as the economic benefits of diffuser cleaning. In addition, mathematic models were applied to simulate the transient oxygen uptake rate (OUR) and show the impact of varying load on OTE and aeration cost, especially when faced with time-of-day power rates. Regular diffuser cleaning can reduce average power costs by 18% and various equalization alternatives can reduce power costs by 6 to 16%.

Analytical methods for quantitative and qualitative determination of hydrocarbons and oil and grease in water and wastewater

Abstract Analytical methods to determine oil and grease concentration and identify specific organic fractions in water and wastewater are reviewed. Important aspects of the development of these procedures are extraction technique, solvent type, and identification and quantification methods for the extracted material. The material presented will assist researchers and regulatory investigators in selecting appropriate analytical procedures and interpreting results.

ASSESSMENT OF AERATION BASIN PERFORMANCE EFFICIENCY: SAMPLING METHODS AND TANK COVERAGE

Abstract A program of oxygen transfer efficiency (OTE) measurements using offgas analysis at the Tillman Water Reclamation Plant (TWRP) in Los Angeles has provided thorough documentation of the performance of fine-pore diffusers in an activated sludge plant. From 1991 to 1993, measurements were made in a uniform pattern that avoided both the ends of the aeration grids and the main pipes along the grid centerlines, which were more likely to be the locations of leaks that could bias the overall average efficiency estimates toward low values. This pattern was chosen in part because of the limited time available during these measurement sessions. When measurements were resumed in 1997 with additional resources, it was decided that several alternatives in sampling should be investigated. First, to assess the significance of the contributions of areas that previously had been avoided, a much more thorough coverage was performed. Second, a new “longitudinal” sampling scheme was tested, as an alternative to the “transverse” approach that had been used previously. This method not only allows making larger numbers of measurements within a similar time, but provides separate results for the left and right sides of a tank. Measurements were also made with the hood in fixed positions for periods of several hours, to check measurement stability and diurnal variation. In addition to the offgas measurements, data on plant operation were recorded from the field instruments and the control room. The data show enhanced efficiencies near the upstream and downstream ends of the grids, and in the areas beyond the ends of the grids. This is at least partly the result of known variations in diffuser fouling, resulting from air flows in the distribution pipes. The longitudinal results show an apparent left–right asymmetry, but this turns out to be an artifact, caused by changing air flows during the measurement session, as shown by the control room data. In the fixed position measurements, variability of several percentage points was observed on relatively short time scales. The plant data also corroborated most of the air flux from the offgas instrument. These observations show the results of going beyond the EPA recommendation to collect offgas from at least 2% of the surface of an aeration basin, particularly when the measurements are planned according to the structure of the air distribution system of the tank. They are steps toward enhancing the importance of OTE monitoring as an input to decisions to clean or repair aeration systems.