Full-scale Water Treatment Research Articles

Rating method for evaluating distribution-system odors compared with a control

A new sensory method was developed and tested at a full-scale water treatment plant. The method evaluates changes in aesthetic water quality during transit in the distribution system. A paired comparison format is used to determine if the odor of a distribution-system sample is different from that of a control sample. The control sample represents the "ideal" water, such as treated water leaving the plant. The method can rapidly determine whether or not a problem exists in the distribution system, and, if one does exist, it allows for characterization of the problem. Over a three-month period a 4-member odor panel evaluated 118 distribution samples by this new procedure. Among the 118 samples tested, 39 samples yielded a consensus among the analysts as to the odor characteristics of the sample; 35 were rated "not different from the control" (about 90%), and only 4 were rated "different from control" (about 10%). The 79 samples for which no consensus was generated had only slight rating differences between analysts and for odor intensity. No taste-and-odor problems were reported by consumers during the time period for this study and the method indicated that no major odor problems existed in the distribution system.

Quantitative assessment of the removal of indicator bacteria in full-scale treatment plants

The elimination of thermotolerant coliforms (Coli44) and spores of sulphite-reducing clostridia (SSRC) in full-scale water treatment was determined by large volume sampling. The objective was to determine the elimination capacity of full-scale treatment processes for micro-organisms, both vegetative bacteria and bacterial spores. In two short-periods in winter and summer, information was collected about the elimination of Coli44 and SSRC by the overall treatment, the contribution of the unit processes and the variability in elimination. Coli44 concentrations in the source waters were reduced by 3.2 to 6.3 log to an average concentration sufficiently low to achieve more than 99% compliance with the drinking water standard. The elimination of SSRC was lower (1.4 to 4.2) and SSRC were observed occasionally (>1%) in finished water by the routine weekly sampling of 100 ml samples. The study also yielded much information about the elimination efficacy of unit processes at the different locations, which enables process optimization and improved process control. Moreover, it is demonstrated that this quantitative information on removal of indicator bacteria by full-scale treatment systems can be used as input for quantitative microbial risk assessment. Further research will be focussed on comparative studies on the removal of faecal indicators and pathogens by unit processes and the improvement of the enumeration methods of pathogens in the source water (recovery efficiencies, specificity).

Influence of surface characteristics on the stability of Cryptosporidium parvum oocysts.

Microelectrophoresis is a common technique for probing the surface chemistry of the Cryptosporidium parvum oocyst. Results of previous studies of the electrophoretic mobility of C. parvum oocysts in which microelectrophoresis was used are incongruent. In this work we demonstrated that capillary electrophoresis may also be used to probe the surface characteristics of C. parvum oocysts, and we related the surface chemistry of C. parvum oocysts to their stability in water. Capillary electrophoresis results indicated that oocysts which were washed in a phosphate buffer solution had neutrally charged surfaces. Inactivation of oocysts with formalin did not influence their electrophoretic mobility, while oocyst populations that were washed in distilled water consisted of cells with both neutral and negative surface charges. These results indicate that washing oocysts in low-ionic-strength distilled water can impart a negative charge to a fraction of the oocysts in the sample. Rapid coagulation experiments indicated that oocysts did not aggregate in a 0.5 M NaCl solution; oocyst stability in the salt solution may have been the result of Lewis acid-base forces, steric stabilization, or some other factor. The presence of sucrose and Percoll could not be readily identified on the surface of C. parvum oocysts by attenuated total reflectance-Fourier transform infrared spectroscopy, suggesting that these purification reagents may not be responsible for the stability of the uncharged oocysts. These findings imply that precipitate enmeshment may be the optimal mechanism of coagulation for removal of oocysts in water treatment systems. The results of this work may help elucidate the causes of variation in oocyst surface characteristics, may ultimately lead to improved removal efficiencies in full-scale water treatment systems, and may improve fate and transport predictions for oocysts in natural systems.

Trihalomethane formation in ozonated and chlorinated surface water

The relatively recent discovery of disinfection by-products has driven the main regulatory organisms to set maximum contaminant levels for certain substances in drinking water. Trihalomethanes can be deemed as the most important group of by-products in chlorinated surface waters. The present work has focused on trihalomethane formation in a full-scale water treatment plant. We studied the effect of several factors, including ozonation, on trihalomethane levels in chlorinated treated water. The treatment scheme also includes an ozonation step.

Practical identification of the dissolved oxygen dynamic in activated sludge plants

This paper presents the application to a full-scale waste water treatment plant (WWTP) of a practical methodology to identify the oxygen supply and consumption terms, which regulate the dynamic behaviour of the dissolved oxygen concentration (S(O)) in activated sludge reactors. This methodology is based on a periodic adjustment of the selected model for oxygen mass-transfer coefficient (K(L)a) and a continuous estimation of the oxygen uptake rate (r(O)), maintaining constant the adjusted K(L)a model, in order to uncouple the effects that the consumption and supply terms have on the S(O) concentration. The adjustment phase of the K(L)a model is based on typified excitations of the system through the aeration system of the plant, which allow the estimation of K(L)a for different values of the aeration intensity parameter, for instance, air flow rate in air diffusion systems, revolution speed in surface aerators, etc. Once the K(L)a model is adjusted, it is possible to evaluate the K(L)a value in process conditions at any time. The continuous estimation of r(O) is carried out starting from the oxygen mass balance in the activated sludge reactor. This practical methodology has been successfully verified in the Badiolegi WWTP in Azpeitia (Spain), which biological process consists of a double stage AB process, with two different aeration systems: fine pore air diffusers in the A-stage and surface aerators in the B-stage.

A method for assessing membrane fouling in pilot- and full-scale systems

This paper introduces a new parameter called the “normalized fouling rate” (NFR), which can be used to analyze data from pilot- and full-scale systems. Analyses of existing data using the NFR parameter have shown it to be a sensitive and reliable method for optimizing operating conditions during piloting and for assessing fouling in full-scale water and wastewater treatment plants. Equations for calculating a cleaning interval (CI) that is the time for a membrane to reach a critical permeability is also presented. The application of this technique is demonstrated with several examples.

The integrated disinfection design framework approach to reactor hydraulics characterization

The integrated disinfection design framework (IDDF) is a new approach to determine disinfection requirements for drinking water treatment facilities. The framework may be applied to enhance or improve disinfection performance in lieu of using the surface water treatment rule (SWTR) Guidance Manual. The overall IDDF approach consists of four modules: hydraulic characterization, disinfectant demand/decay, inactivation kinetics, and disinfection by-product (DBP) formation. In this study, a review of the hydraulic characterization module is presented. The module was applied to two full-scale water treatment plant processes (1: a group of six filter beds, 2: a disinfection contactor). The data from the hydraulic characterization module, which consists of three methods to generate the residence time distribution (RTD) curve, was then used to demonstrate the microbial inactivation and DBP formation level that might be produced at the process effluent. Results suggest that the predicted microbial inactivation level is sensitive to the hydraulic characterization method. However, all three methods predict very similar DBP formation despite differences in the RTD data. Results also showed that the disinfectant dose applied to the contactor could be reduced by 35% and still maintain the same credit for Giardia inactivation specified by the USEPA CT tables. This reduction in disinfectant dose could result in a reduction in the total trihalomethane (TTHM) level by 10% and haloacetic acids (HAAs) by 20%.

Changes in GAC pore structure during full-scale water treatment at Cincinnati: a comparison between virgin and thermally reactivated GAC

During full-scale water treatment operation at the Richard Miller water treatment plant (Cincinnati, Ohio) we frequently evaluated the changes in pore volume distributions of a reactivated (F-400) granular activated carbon (GAC), as compared with that of its virgin counterpart. The reactivated GAC had experienced six cycles of water treatment and thermal reactivation. The reactivated GAC was slightly more effective at removing TOC (total organic carbon) than was the virgin GAC during the first half-year of service. Yet, the pore size distributions of the two GACs were very different. The virgin GAC was mostly microporous, with less mesopores. Conversely, the reactivated GAC was mostly mesoporous, with less micropores. For the virgin GAC, adsorption changed the volume of pores below 50 Å in width most significantly, and there was minor change in pores larger than 50 Å. In contrast, the reactivated GAC showed the greatest volumetric change in pores that were 100 to 500 Å in width.

Characteristics of alumino-humic flocs in relation to DAF performance

This paper examines the implications of pretreatment in the context of the likely behaviour of flocs in DAF units. Evidence indicates that the maximum floc size (dmax) of alumino-humic is scaled by the Kolmogorov length (eta) with dmax/eta approximately 1. A larger ratio exists when polymer is present. Data from the literature suggests that velocity gradient in the inlet chamber may exceed 1000 s-1, suggesting eta approximately 40 microns. This view of the response of floc to shear is supported by shear tests carried out on samples of floc withdrawn from flocculators at full scale water treatment works. Using an underwater CCTV camera, coupled with image analysis, it is shown that floc sizes in conventionally designed flocculators are much bigger than the sizes which are likely to exist in DAF units. Circumstantial evidence gained from water treatment works suggests that DAF units perform satisfactorily whatever the size of the incoming floc. From such evidence, the authors question the conventional design of the flocculators in association with DAF units.

Influence of molecular weight distribution of organic substances on the removal efficiency of DBPS in a conventional water treatment plant

The objective of this study is to investigate how the molecular weight distribution of the organic substances affects their treatment efficiencies and the reduction of disinfection by-products (DBPs) in the various unit operations of a full-scale water treatment plant. The results indicate that the membrane with a smaller molecular weight cut-off is more effective for removing the organic substances and its associated water quality parameters from the raw water. For example, using the membrane with a molecular weight cut-off of 0.5 K (500 daltons), the removal efficiency of DOC from the raw water sample can be as high as 88%. Removal efficiencies of other water quality parameters such as UV254 absorbance, THMFP and AOXFP are generally between 65–69%. When undergoing the various unit operations in the conventional water treatment plant, most organic substances are removed in the coagulation process followed by sedimentation.

Removal of sulphite-reducing clostridia spores by full-scale water treatment processes as a surrogate for protozoan (oo)cysts removal

At eight full-scale water treatment plants in the Netherlands the removal of spores of sulphite-reducing clostridia (SSRC) was determined. By sampling and processing large volumes of water (1 up to 500 litres) SSRC were detected after each stage of the treatment. This enabled the assessment of the removal efficiency of the full-scale unit processes for persistent micro-organisms. A comparison with literature data on the removal of Cryptosporidium and Giardia by the same type of processes revealed that SSRC can be considered as a potential surrogate. The average Decimal Elimination Capacity (DEC) of the overall treatment plants ranged from 1.3–4.3 log. The observed actual log removal of SSRC by the unit processes and the overall treatment at one of the studied locations showed that the level of variation in removal efficiency was approximately 2 log. Moreover, from the actual log removal values it was observed that a low SSRC removal by one unit process is partly compensated by a higher removal by subsequent unit processes at this location. SSRC can be used for identification of the process conditions that cause variation in micro-organism removal which may lead to process optimization. Further research is necessary to determine the optimal use of SSRC in water quality monitoring for the production of microbiologically safe drinking water.

Survival of Bacteria After Ozonation

The change of the bacterial population after each water treatment process was examined in a full-scale water treatment plant that uses ozone as a primary disinfectant. The fluctuation of heterotrophic bacterial number along the water treatment processes was determined. After ozonation, the bacterial number decreased to 13 CFU/mL. The surviving bacteria after each water treatment process were identified to genus or species level. The significant finding was the predominance of double-layered gram-positives (75%) among the surviving bacteria after ozonation. It included Mycobacterium spp., Bacillus spp., Corynebacterium spp., and Micrococcus spp. On the other hand, the dominance of gram-negatives was observed in most other water samples but each treatment process exerted different selection on dominant bacterial groups. The proportion of opportunistic pathogens was the lowest in the ozonated water.

Simulating the effect of blanket characteristics on the floc blanket clarification process

Previous attempts at simulating the floc blanket clarification process have failed to predict adequately the performance of ‘real’ tanks on water treatment works over a range of treatment conditions. In this paper, a mathematical model of the floc blanket clarification process is presented. This model has been used to simulate the performance of a flat-bottomed clarifier operating on a full-scale water treatment works. The model predictions have been compared with data obtained from the treatment works, and the model has been shown to perform well. The model has then been used to simulate the effects of changes in the operating conditions of the clarifier on the concentration of the blanket in the clarifier and the quality of the treated water. The importance and potential uses of a model of the process at a treatment works are discussed.

Simulating the effect of blanket characteristics on the floc blanket clarification process

Previous attempts at simulating the floc blanket clarification process have failed to predict adequately the performance of ‘real’ tanks on water treatment works over a range of treatment conditions. In this paper, a mathematical model of the floc blanket clarification process is presented. This model has been used to simulate the performance of a flat-bottomed clarifier operating on a full-scale water treatment works. The model predictions have been compared with data obtained from the treatment works, and the model has been shown to perform well. The model has then been used to simulate the effects of changes in the operating conditions of the clarifier on the concentration of the blanket in the clarifier and the quality of the treated water. The importance and potential uses of a model of the process at a treatment works are discussed.

Adsorption of microcystin-LR by activated carbon and removal in full scale water treatment

Removal of microcystin toxins from drinking water was evaluated at two full scale treatment plants that employed coagulation-sedimentation, dual media filtration and chlorination combined with either granular activated carbon filtration or powdered activated carbon. The influence of natural organic matter on the adsorption of the cyanobacterial toxin, microcystin-LR, by activatedcarbon was also evaluated in laboratory studies over a range of toxin concentrations similar to those typically observed in raw water at these plants. The sensitive protein phosphatase inhibition bioassay was used to quantify microcystin. Conventional treatment processes combined with activated carbon generally removed more than 80% of microcystin from raw water, but a residual concentration of 0.1-0.5 μg equivalents of microcystin-LR per liter was observed considering both (GAC and PAC) treatment facilities. Most values of residual microcystin-LR were at the low end of this range, but the upper end approaches the guidance level being considered by Health Canada for these toxins in drinking water

Effect of Pre-Ozonation on Removal of Organic Matter during Water Treatment Plant Operations

Pre-ozonation altered removal of organic matter during bench or full-scale water treatment through two main effects. First, pre-ozonation directly removed organic matter by mineralization, volatilization and/or stripping reactions, improving removal in comparison to unozonated systems. On the other hand, pre-ozonation decreased the surface charge of floc formed after coagulation with hydrolyzable metal salts, hindering adsorptive removal of the anionic organic molecules by floc surfaces and/or inducing stabilized floc formation; changes that decrease removal in comparison to unozonated systems. The relative importance of the two effects determined whether pre-ozonation enhanced or hindered removal of organic matter. In most water treatment plants pre-ozonation is predicted to have an adverse effect on physical removal of organic matter at ozone doses above about 0.7 mg O3/mg TOC, while enhanced removal may occur if relatively high concentrations of volatile organic matter are present. In ancillary results, pre-ozonation hindered turbidity removal and increased the concentration of coagulant metal residuals in finished drinking water at low coagulant doses.

Studies of dual‐media filtration of the Tigris River used for drinking water. Mathematical relationships

Abstract The use of dual media filtration for treating Tigris River raw water is considered a new technique in Iraq. More than forty test runs employing different dual media filter configurations were conducted. A pilot plant designed to operate similarly to the full scale water treatment plant was used for this purpose. The results were statistically analyzed and a mathematical equation describing the relationship between involved variables was developed. The relative strength of each independent variable upon the effluent quality was also revealed.

Comparison of Ozone and Oxygen Mass Transfer in a Laboratory and Pilot Plant Operation

Abstract Mass transfer of ozone and oxygen to water was investigated both in pilot plant countercurrent bubble column and in a Rushton type laboratory stirred reactor supplied with a variable speed turbine agitator. A comparison was made for different hydrodynamic conditions with the main task of developing an engineering approach for determination of the physical volumetric mass transfer coefficient (KL oa), specific interfacial area (a), and physical masstransfer coefficient (KLO). The mass transfer characteristics of ozone and oxygen can be determined quickly in a pilot plant or laboratory apparatus, and employed to optimize the performance ofthe full scale water treatment plant.

The Taman Process: Experiences of Full-Scale Operation at Anjala Paper Mill

The first full-scale anaerobic waste water treatment plant in the Finnish wood processing industry has been completed at Anjala Paper Mill. This TAMAN process together with the extensive renewal of the water circulation systems as well as solids recovery have made it possible to meet the new environmental requirements coming into force in June 1987. The total BOD7 reduction due to this investment program is nearly 90 %. The waste water flow through the TAMAN process is 11000 m3/d. The specific water consumption of the debarking plant has been minimized and circulation water is clarified in a separate settler. TAMDEC gravity thickeners make solids retention more effective and the TASSTER screw press ensures that all the mill's sludge is dewatered before fluidized bed incineration.

Mutagenic activity of disinfection by-products.

Data on raw water quality, disinfection treatment practices, and the resulting mutagenic properties of the treated water were compiled from pilot- and full-scale treatment experiments to evaluate that parameter which might produce variability in the results of a mutagenic study. Analysis of the data and comparison of treatment practices indicated that the measured mutagenic activity is strongly related to the characteristics of the organic matter in the raw water, the methodology used to sample and detect mutagens, the scale of the study both in terms of treatment flow and period of study, and the point at which and the conditions under which oxidants are added during treatment. Conclusions regarding disinfection systems in full-scale water treatment plants include the following: When raw water is pretreated and high concentrations of organics are present in the raw water, both ozonation and chlorination increased mutagenic activity. However, no significant difference in mutagenicity was found between the two oxidants. Both in the case of a nitrified groundwater and a clarified surface water, the mutagenic activity of the water after ozonation was related to its mutagenic activity before ozonation. With ozonation, mutagenic activity decreased after granular activated carbon (GAC) filtration. Thus, when GAC filtration follows ozone disinfection, early addition of oxidants may not be deleterious to the finished water quality. When chlorine or chlorine dioxide is added after GAC filtration, chlorine dioxide was found to produce a less mutagenic water than chlorine. Although these conclusions suggest means of controlling mutagenic activity during treatment, it must be stressed that the measurement of mutagenicity is a presumptive index of contamination level.