Clifford W. Randall

Is it PAO-GAO competition or metabolic shift in EBPR system? Evidence from an experimental study

Reduced EBPR performance in full and bench-scale EBPR studies was linked to the proliferation of GAOs but often time with the lack of any evidence. In this study, a detailed enzymatic study was coupled with batch tests and electron microscopy results for a realistic explanation. The results eliminated the possibility of population shift from PAO to GAO or other non-PAO due to the short batch test period provided which would not allow a population shift and further justified with the electron microscopy results. The results indicate that glycogen serves not only as source of reducing power for PHA production but also serves as an alternative energy source when the poly-P pool of the PAOs is depleted. Slow generation of ATP via glycolytic pathway at 5 degrees C cannot satisfy energy requirements of EBPR cells to complete several cell functions including acetate uptake and PHA storage. However, the glycolytic pathway is efficiently operable at warm temperatures (> 20 degrees C). The reduced performance of enhanced EBPR facilities operated at warm temperature may not be a result of GAO proliferation; instead it may be related the efficient use of the glycolytic pathway by PAOs which results in more glycogen storage and less P uptake, thereby reducing the EBPR performance.

Waste activated sludge conditioning by direct slurry freezing

Abstract It has been widely observed and noted that waste sludges subjected to freezing undergo a conditioning effect that greatly enhances subsequent dewatering. However, wide-spread application of freezing for conditioning purposes has never been practiced because of the high operating costs associated with conventional indirect freezing systems. Furthermore, all reported efforts involved the solid freezing of the experimental sludge. The purpose of this research was to evaluate the technical and economic feasibility of waste activated sludge conditioning for dewatering using a direct slurry freezing system. Liquid butane was used as the refrigerant and it was bubbled through the liquid sludge to form an ice-sludge slurry. Economic investigation included butane recovery techniques. The results of the investigation showed that the dewaterability of waste activated sludge can be greatly improved by slurry freezing with liquid butane. Slurry freezing results in better conditioning and a better quality supernatant than does solid freezing because fewer cellular solids are destroyed by the freezing pressure. The conditioning effect is also comparable to or better than conditioning by widely used processes such as heat treatment. Furthermore, recovery of butane for subsequent reuse reduces the cost of slurry freezing to less than the cost of nearly all conditioning processes in current use.

Phosphorus removal in the activated sludge process

Abstract The results from this research suggest that both calcium phosphate precipitation and enhanced biological uptake play a role in phosphorus removal in the activated sludge process when a non-nitrifying, anaerobic-aerobic system is used to treat a low calcium wastewater. The primary removal mechanism was found to be biological uptake, as calcium phosphate precipitation accounted for only 15–27% of the total phosphorus removed. Calcium phosphate precipitation in the aerobic unit was enhanced because of the pH increase in that reactor. This was the result of low CO2 production (indicated by low specific oxygen uptake values) and intense aeration which caused excessive CO2 stripping in the aerobic unit

Efficient design of stormwater holding basins used for water quality protection

Abstract By quantifying and taking advantage of the first flush phenomenon it is possible to develop a rational method for the design of stormwater basins based on the retention of a predetermined fraction of the pollutant load leaving a catchment. Such a procedure is applicable to the design of basins for small ( The data required for this design procedure is usually not available for most sites. Such data is both difficult and expensive to gather. However, as more data is obtained, it may be possible to develop generalizations among watersheds with regard to loading curves which are based on land use similar to land use groupings developed for the runoff coefficient “C”. Further, it may be possible to develop generalized timing curves for other pollutants. These curves are helpful in describing the runoff process and their development would provide additional capability in predicting the performance of stormwater basins. It is anticipated that the use of this method of design could result in substantially smaller basins being required for water quality protection in urban areas than would be the case if they were designed based strictly on the volume of runoff expected.

THE IMPACT OF ATMOSPHERIC CONTAMINANTS ON STORM WATER QUALITY IN AN URBAN AREA

Summary Composite precipitation samples were collected by recording raingages at nine stations in the Virginia portion of the greater Washington, D.C. metropolitan area. The samples were analyzed for COD, TOC, all nitrogen and phosphorus forms, and seven heavy metals; iron, zinc, lead, copper, cadmium, chromium and manganese. The results showed that wash out of the atmospheric contaminants occurred during the early stages of precipitation events, and that these contaminants are present in sufficient quantity to have a significant impact on surface water quality. Samples tended to contain similar amounts of pollutants after the same rainfall event regardless of land use location and distance from the center city up to 33 miles. Ranking techniques indicated, however, that precipitation in agricultural and land disturbance areas tends to contain more nutrients. Principal factors affecting the total quantity of pollutants in rainfall are atmospheric conditions (stagnant or turbulent) and antecedent conditions (time since previous precipitation event).

FACTORS AFFECTING BIOLOGICAL PHOSPHORUS REMOVAL FOR THE VIP PROCESS, A HIGH-RATE UNIVERSITY OF CAPETOWN TYPE PROCESS

ABSTRACT The phosphorus removal capabilities of the Virginia Initiative Plant (VIP) process, a high-rate biological nutrient removal (BNR) process, are presented and compared to the high-rate A2/0 and the low-rate University of Capetown (UCT) processes. The results indicate superior phosphorus removal capability for the VIP process compared to the A2/0 and UCT processes. In general, VIP process phosphorus removal was maximized by operation at the lowest possible total process mean cell residence time (MCRT) and with an aerobic hydraulic residence time (HRT) not exceeding 4 hours. A total process MCRT of 5 days provided acceptable nitrogen removal and excellent phosphorus removal for wastewater temperatures of 20°C or above, while a total process MCRT of 20 days would be required at a temperature of 12°C. Operation of the VIP process at an aerobic HRT greater than 4 hours apparently resulted in oxidation of stored organic matter that adversely affected phosphorus uptake kinetics. Data analysis suggested that the VIP process could have been operated at an anaerobic HRT as short as 20 minutes. Superior phosphorus removal performance was observed for the VIP process compared to the A2/0 process when the BOD5/TPO4 ratio of the wastewater was significantly less than 20.

Denitrific ation of a high ammonia leachate using an external carbon source

Abstract A single‐sludge, nitrification‐denitrification system was used to treat a high ammonia (170–230 mgL−1), low biodegradable carbon (B0D5 = 10–40 mgL−1) landfill leachate. Glucose and methanol were used as external carbon sources for denitrifi‐cation. Complete ammonia removal was consistently achieved; when glucose was used as the carbon source, inconsistent denitrification performance was experienced (fluctuated between 10–100%). However, with methanol, the denitrification performance was consistent and reliable, with complete denitrification achieved.

The effect of iron dosing on reducing waste activated sludge in the oxic-settling-anoxic process

This study evaluates the biological solid reduction in a conventional activated sludge system with an anoxic/anaerobic side stream reactor receiving 1/10 of return sludge mass. Influent iron concentrations and feeding modes were changed to explore the consistency between the influent iron concentration and yield values and to assess the impact of feeding pattern. The results indicated that sludge reduction occurs during alternately exposure of sludge to aerobic and anoxic/anaerobic conditions in a range of 38-87%. The sludge reduction values reached a maximum level with the higher iron concentrations. Thus, it is concluded that this configuration is more applicable for plants receiving high iron concentrations in the wastewaters.

Effects of pH and substrate on the competition between glycogen and phosphorus accumulating organisms

Abstract This article evaluates effects of pH and substrate on the competition between glycogen (GAOs) and phosphorus accumulating organisms (PAOs). A sequencing batch reactor system was operated for enhanced biological phosphorus removal (EBPR) with acetate as the sole carbon source and acetate added domestic wastewater at different influent acetate/phosphate ratios. Some batch tests were performed using acetate added domestic wastewater at different influent acetate/phosphate ratios, with different initial pH values of acetate and domestic wastewater mixture. The resulting experimental data supported the presence of GAOs for all tested HAC/P ratios, especially under P limiting conditions for acetate as sole carbon source. Strong evidence is observed that acetate added domestic wastewater system had higher PAOs fraction than acetate system as sole source carbon, with using model components, namely substrate uptake, glycogen utilization and P release.

The stimulation of filamentous microorganisms in activated sludge by high oxygen concentrations

A laboratory study was conducted to compare the response of an activated sludge culture proliferating in an environment where the DO concentration was maintained between 8-9 mg l−1 to that of a culture in an environment where the DO concentration was 2 mg l−1 when both systems were subjected to identical loading fluctuations. It was observed that in the high DO system, filamentous microorganisms became the predominate form when the suspended solids concentration dropped below a value near 4000 mg l−1. However, no filamentous growth appeared in the alternate system until the suspended solids level dropped below 500 mg l−1. A model is developed which proposes to explain this observation.