Anthony G. Collins

Preozonation as an aid in the coagulation of humic substances—Optimum preozonation dose

Abstract Using a number of commercial and natural water humic substances, the positive effect of preozonation as an aid to coagulation-flocculation of these compounds was confirmed by a 13–30% decrease in alum consumption. Experiments were conducted at a pH of 5.5 and humic substance concentrations of 20 mg/l (total organic carbon concentrations of approx. 10 mg/l). Standard jar test procedures were used to evaluate alum dosage requirements and the primary water quality parameters monitored were turbidity, u.v., TOC and color. In addition to decreased alum consumption the existence of an optimum preozonation dose (OPD) was also confirmed. For ozone dosages beyond the OPD, the benefit is reduced, then eliminated and further ozonation becomes detrimental to the coagulation-flocculation removal process. The OPD was found to be a function of the initial colloidal charge density (CCD) of the humic substances. The strong correlation of initial CCD to the OPD identified the major mechanism for preozonation to be effective as a reduction in CCD due to mild ozonation. Preozonation did not show a positive effect on a system with very low molecular weight (noncolloidal) humic substances.

Ultra-rapid freezing of water treatment residuals

An alum water treatment residual (“sludge”) was conditioned by freezing at ultra-rapid rates. Ultra-rapid rates were obtained by freezing on liquid nitrogen. The purpose of the experiments was to determine the conditions necessary for such rapid freezing to improve dewaterability. Contrary to results reported in the literature, ultra-rapid freezing worked extremely well. Although the conditioned flocs (“zots”) were not as dense or granular as obtained at slower freezing rates, dewaterability was still greatly improved. Dewaterability, as measured by cake solids content (CSC), capillary suction time (CST), filterability coefficient (χ) and aggregate volume index (AVI), was best for samples with an initially high solids content and for samples that had been cured or stored at sub-freezing temperatures, for long times. Zot size analyses showed that zots decreased in size following ultra-rapid freezing. The results are explained using a proposed conceptual model of the residuals freezing process.

Information processing coupled with expert systems for water treatment plants

Abstract The water utility industry is facing increased pressures to produce higher quality finished water at lower costs. The traditional feedforward-feedback control systems used in water treatment plants can be enhanced by using predictive models (with feedforward control) and diagnostic expert systems (with feedback control). The use of predictive models is advantageous as it is virtually impossible to ascertain specific chemical dose requirements from measurements of raw water quality parameters. These predictive models may be either regression relationships or neural networks. When feedback data indicate that the finished water quality is not acceptable and usual corrective actions based on feedback from sensors fails to correct the situation, diagnostic expert systems can be effectively used to aid operator decision making.

A novel approach to ozone ‐ water mass transfer using hollow ‐ fiber reactors

Abstract A novel reactor system based on microporous hollow‐fiber membranes is proposed for ozone‐water systems. Results from experimentation, where ozone transfer is achieved via the hollow fibers into a closed circuit flow‐through reactor configuration, indicate such systems may be superior to existing ozone transfer approaches.

An Alternative Approach to Gas Phase Ozone Determination

Abstract A pragmatic, real time procedure to determine gas phase ozone concentration is presented. The procedure requires syringe extraction of an air-ozone sample via a Teflon septum followed by ozone measurement using the indigo method. The results are confirmed by comparison to the standard iodometric technique. The method has a number of potential applications, including as an alternative to continuous gas phase UV monitoring, if UV absorbing compounds other than ozone are present.

Assessing Sediment Accumulation in a Eutrophic Lake in Northern New York

ABSTRACT We determined the pattern, rate, and extent of deposition of bulk sediments and sediment-bound phosphorus (P) in Black Lake. Vertical gradients in total phosphorus (TP) and 137Cs often were irregular within cores and variable among cores, reflecting sediment disturbances including bioturbation, resuspension, and lateral transport. Surface sediments exhibited a horizontal spatial gradient in TP content, with P levels that declined downstream from the lake inlet, which reflected a large input of settleable P from the primary tributary. Sediment 137Cs and TP data suggested an average lake-wide sediment accumulation rate of approximately 0.6 cm yr−1 since the early 1960s and greater accumulation of TP in 1975–90 than during 1960–75. The mean depth of sediment accumulation over bedrock was estimated to be at least 3.6 m. These data indicate the contemporary rate of water depth decrease due to sediment accumulation in Black Lake is much greater than the lakes postglacial average, and the rate of sedim...

Preozonation To Improve And Optimize Diatomaceous Earth Filtration

The benefits of preozonation before diatomaceous earth filtration have been demonstrated in a City of New York research program to develop design criteria for treatment of its 300 mgd Croton water supply. In the treatment of a supply where paniculate matter is predominantly of organic origin, preozonation provides two outstanding advantages that are not possible in diatomaceous earth filtration alone.

A STOCHASTIC APPROACH TO CHEMICAL DOSAGE REQUIREMENTS FOR SMALL TREATMENT PLANTS

ABSTRACT To aid operators at small treatment utilities, a stochastic method for determining alum dosing is presented. Using a multiple regression analysis, it was found that the alum dosage level can be predicted from previous alum doses, raw turbidity, and seasonal effects. From the fitted model it is also possible to assign dosage levels based upon the risk of underdosing. By basing treatment decisions on statistical models of previous successful treatment operation, plant efficiency will be maximized resulting in fewer plant upsets and more consistent water quality.