W. Wesley Eckenfelder

Effluent quality variation from multicomponent substrates in the activated sludge process

Abstract The objectives of this investigation were: (1) to examine the overall substrate removal of a three component mixture by an acclimated seed using total organic carbon measurements, (2) to observe the rates of removal of each of the three components in the mixture at four different food-to-microorganism ratios (F/M), (3) to show the effects of the composition of the substrate with varying degradability on effluent quality, and (4) to observe the effects of sludge age on total substrate removal. To accomplish these objectives, sludge from a municipal sewage treatment plant was acclimated as seed in a continuous flow, completely mixed laboratory reactor. A multicomponent substrate consisting of a mixture of glucose, phenol and sulfanilic acid, was fed at different F/M ratios. The removal rate was determined as total organic carbon and specific analytical measurements for each substrate in the influent and effluent samples were also made. Various combinations of glucose, phenol and sulfanilic acid were used as a substrate in three runs. This made it possible to observe the removal rate of each substrate in the mixture as related to their individual biodegradability as well as their influent concentrations. The results showed that for the three substrates employed in this study, the overall removal rate, in terms of total organic carbon in a mixed acclimated culture, is the sum of the individual specific removal rates. The effluent quality in terms of soluble TOC was related to the F/M or to the sludge age using Eckenfelders kinetic model.

Modifications to aerobic digestor design

Abstract Generally, aerobic digestion of biological sludges is conducted in completely-mixed aeration basins. Although first-order kinetics have classically been used to predict and design aerobic digestors, it is shown that these models will result in underdesign and that a model based on a mass balance around the digestor more accurately predicts digestor performance. The experimental work discussed herein demonstrates that a first-order rate coefficient, determined under batch conditions, can be employed in the completely-mixed model for design purposes. Certain design constraints are discussed, such as laboratory scale-up, temperature, etc. A design example is illustrated using the approach presented herein.

The effect of inorganic salts on the activated sludge process performance

Abstract The effect of inorganic salts such as sodium chloride and sodium sulfate on the performance of the activated sludge process was examined. When proper acclimation procedures were followed, the adverse effects of salts on the process were minimized. One of the parameters monitored, effluent suspended solids, had very low values (less than 10 mg l −1 ) up to an inflow sodium chloride concentration of about less than 35 gl −1 . The chemical oxygen demand of the effluent increased steadily with increasing sodium chloride concentrations, but biochemical oxygen demand values remained very low (less than 5 mg l −1 ) which indicated that the increase in chemical oxygen demand was due to the portion that cannot be degrated biologically. The effect of sodium sulfate on the system was even less profound. In addition to the effluent being very clear and low in suspended solids, the chemical oxygen demand removal efficiency remained high.

The activated sludge process: State of the art

The activated sludge process has been employed for the treatment of municipal and industrial wastewaters for many years. Modifications and improvements to the process have been the result of extensive research from both a theoretical and practical viewpoint. This article reviews the activated sludge process as it is presently applied. Design approaches are developed including examples for both municipal and industrial wastewaters. Special consideration for industrial wastewaters are discussed. Process modifications including nitrification denitrification and priority pollutant removal are considered.

Response of dissolved oxygen to changes in influent organic loading to activated sludge systems

Abstract The major objective of this investigation was to examine the response of the activated sludge process to transient organic loadings and to evaluate the applicability of dissolved oxygen (DO) concentration and oxygen uptake rate as process control variables. A modified laboratory-scale activated sludge unit was used to continuously measure the ambient dissolved oxygen level. The change of the dissolved oxygen concentration responded to variations in the influent composition of the wastewater. First, the system was maintained at steady-state and system variables were measured for soluble TOC, MLVSS and oxygen uptake rate. The organic shock loading was induced by increasing or decreasing the baseline feeding of TOC concentration. As soon as a transient loading occurred the DO levels in the system were continuously monitored with the DO analyzer. A simplified material balance equation for dissolved oxygen in the system was developed and the dynamic behavior of oxygen uptake rate was examined. It was demonstrated that under transient conditions the changes in the dissolved oxygen concentration reflected the variations in the exogenous respiration rate of the biomass in the system due to fluctuations in the influent waste characteristics. Based upon the rapid response to the shock loading and the correlation of the change in the DO level to the magnitude of the shock loading, the two variables (DO concentration and oxygen uptake rate) generated from this biological monitor showed potential as a control variable for the activated sludge process.

Relationships between organic loading and zone settling velocity in the activated sludge process

Abstract The performance of the activated sludge process is functionally dependent on the settling and compaction properties of the activated sludge. The settling properties of activated sludges vary markedly depending on the presence or absence of filamentous organisms and on the process operating conditions. In this study the process was operated to minimize the presence of filamentous organisms and to investigate the effects of operating process variables, mainly organic loading. It was found that over the range of organic loadings tested, the ZSV increased with organic loading due to the size of the sludge floc which was also directly proportional to the organic loading. The ZSV in aerobically digested sludge was found to decrease with sludge age.

Development of a continuous respirometer

Abstract A continuous oxygen uptake meter or continuous respirometer was developed which produced a rapid and reliable response to systemic shocks. The respirometer basically is a 101. Plexiglas laboratory activated sludge unit with a variable volume air tight side car. The feed enters the completely mixed aeration basin and is pumped into the side car. The side car is the site of the oxygen uptake measurements as indicated by a continuously monitoring dissolved oxygen probe. The system was most sensitive to changes in influent concentrations when run at an F / M = 0.1. Response time for a change in DO of 0.1 ppm was less than 4 min. The continuous respirometer was tested employing both synthetic and raw industrial wastes.

The effects of sludge age and metal concentration on copper equilibrium in the activated sludge process

Abstract This research investigated the general effects and equilibrium behavior of copper in the activated sludge process under a range of organic loadings and influent copper concentrations. This was achieved in a two‐phase experiment using continuous‐flow laboratory scale activated sludge units.

Estimating oxygen requirements and waste sludge from activated sludge with and without primary clarifiers treating municipal wastewater

Abstract Many municipal activated sludge plants operate without a primary clarifier. Depending on the SRT of the system, this will markedly affect both oxygen requirements and sludge production as compared to the use of a primary clarifier. A design procedure and an example is presented to compute oxygen requirements and sludge yield with and without the use of primary clarifiers.

A new design procedure for activated sludge based on active mass

Abstract Design equations are formulated for the activated sludge process based on degradable and non‐degradable fraction of the mixed liquor volatile suspended solids. By appropriate mass balances relationships are developed for the degradable and active fractions based on sludge age. These relationships are in more usable form than previous relationships based on F/M ratio. Incorporation of the active fraction in kinetic design equations is shown to result in more accurate estimates of excess biological solids generation and required hydraulic residence time