Scale Wastewater Treatment Plant Research Articles

Description and test of a new geneation of nutrient sensors

Sensor prototypes for measurement of ammonium, nitrate and phosphate in wastewater treatment plants are described together with the results obtained in laboratory and pilot scale wastewater treatment plants. A functional description of the sensor principles is presented together with the installation and operation procedures. Basically the measurements are done using membrane technology in combination with semi-micro Continuous Flow Analysis (μCFA) with classic colorimetry. Because of this the sensors can be installed directly in the aeration tanks without any need for sampling, filtration, etc. Furthermore, the semi-micro scale is used in such a way, that handling of chemicals and waste is a closed loop in a package to be changed once a month. The sensors have been tested thoroughly in a pilot scale waste water treatment plant (recirculation) using real raw wastewater as well as artificial wastewater. The sensors have been placed directly in the aeration tank or in the anoxic tank of the pilot plant. The tests show very little, if any, fouling problems due to the membrane material used. The test results show a good reproducibility and most important, compared to other available sensors/analyzers on the market, very low response times, less than 5 minutes. Owing to these low response times, experiments with direct measurement of nitrification and denitrification rates were carried out.

Knowledge based diagnosis of solids-liquid separation problems

Often the suspended solids concentration in activated sludge treatment plants may display both large amplitudes and unnaturally fast changes. If the sensor calibration has been found satisfactory, the abnormal appearance has to be explained by the process itself. There may be three principal reasons for such a behaviour. severe hydraulic conditions, poor floc separation properties or very high sludge blanket. During these circumstances it is very informative to qualitatively examine the relationships between the suspended solids concentration variations and important influencing variables, such as the flow rates and the sludge blanket level. This kind of knowledge based diagnosis is superior to dynamic models for such odd behaviour. A simple on-line method to perform the diagnosis is presented. The method has been tested on a massive set of data from a full scale wastewater treatment plant in Sweden and shown unexpected good ability to supply early warnings. It is also shown that small hydraulic disturbances may purposefully be injected into the settler in order to analyse the risk for process failure.

Knowledge based diagnosis of solids-liquid separation problems

Often the suspended solids concentration in activated sludge treatment plants may display both large amplitudes and unnaturally fast changes. If the sensor calibration has been found satisfactory, the abnormal appearance has to be explained by the process itself. There may be three principal reasons for such a behaviour: severe hydraulic conditions, poor floc separation properties or very high sludge blanket. During these circumstances it is very informative to qualitatively examine the relationships between the suspended solids concentration variations and important influencing variables, such as the flow rates and the sludge blanket level. This kind of knowledge based diagnosis is superior to dynamic models for such odd behaviour. A simple on-line method to perform the diagnosis is presented. The method has been tested on a massive set of data from a full scale wastewater treatment plant in Sweden and shown unexpected good ability to supply early warnings. It is also shown that small hydraulic disturbances may purposefully be injected into the settler in order to analyse the risk for process failure.

Cold Climate Sequencing Batch Reactor Biological Phosphorus Removal – Results 1991-92

The aeration tank in a small scale wastewater treatment plant was converted to a sequencing batch reactor (SBR) with a maximum volume of approx. 27 m3. The main purpose of this study was to examine low temperature biological phosphorus removal (BPR). The wastewater temperature varied during the study between 3 and 8°C, with a water temperature at or below 5°C during 7 months of the year. The SBR unit has been in operation from the end of 1989, the study period discussed here covered July 1991 - December 1992. SBR cycle time was varied between 6 and 12 hours, giving a total daily treatment capacity of between 18 and 36 m3. The influent biological oxygen demand - 7 days (BOD7) levels varied between 88 and 165 mg/l. Corresponding phosphorus levels were between 3.10 and 9.55 mg/l The mean effluent level of phosphorus was 1.57 mg/l and the BOD7 value was 23 mg/l. This gives a mean total phosphorus reduction of 74% and a BOD7 reduction of 81 %. During the study, mean supernatant suspended solids (SS) levels were quite high, at around 36 mg/l. This high SS level contributed a major part of both outlet phosphorus as well as BOD7 value. Effluent soluble values for phosphorus and BOD7 were 0.79 mg/l and 9 mg/l. The supernatant SS component of BOD7 and phosphorus increased at lower temperatures. It was not possible to reduce or balance this increase by increased cycle time or increased settling time within the maximum cycle time available (12 hours). Stable low supernatant phosphorus and BOD7 levels are thus to a large degree controlled by the effluent SS level. A maximum of 20 mg/l supernatant SS is necessary to reach target supernatant values of less than 1 mg/l of phosphorus and 15 mg/l of BOD7.

Relationship for Clarification Efficiency of Circular Secondary Clarifiers

This paper discusses a regression-based model describing clarification efficiency of circular activated sludge secondary clarifiers. Surface overflow rate was found to be well correlated with effluent suspended solids, sidewater depth and settled sludge volume at three full scale wastewater treatment plants during a six month study. Relationship was verified to be sufficiently accurate for prediction of effluent suspended solids concentration over a six month period at another three treatment plants.

Anaerobic-Aerobic Wastewater Treatment Plant of a Potato Chips Factory

The described full scale wastewater treatment plant of the potato chips factory is working with a two-stage anaerobic pretreatment followed by an aerobic purification with nitrogen and phosphorus removal. Extraordinary elements of the plant are the fixed-film methane reactor and the trickling filter used as a cooling element between the anaerobic stage and the activated sludge system. A sludge blanket was built up underneath the swimming support media of the fixed-film methane reactor. During the first year of operation the energy profit by methane production was 1 056 000 kWh, which is 50 % of the whole energy consumption of the wastewater treatment plant.

Test of the Activated Sludge Model's Capabilities as a Prognostic Tool on a Pilot Scale Wastewater Treatment Plant

A newly developed simulation programme, based on the Activated Sludge Model No. 1, was used to investigate the model's abilities to predict variations in a Bio-Denipho pilot plant. The model was tested under both normal conditions and in connection with an inhibition incident on the pilot plant with positive results.

Experiences of Self-Tuning Control of an Activated Sludge Process

This paper discusses experiences in implementing self-tuning dissolved oxygen concentration control in a full scale wastewater treatment plant. After presentation of the control structure, the performance is discussed. Then a number of special problems are considered. The most serious one is a severe limitation in the air supply to the aerators. Other problems are mode transitions from manual to automatic mode and handling of large changes in the process output.

The Operation and Maintenance of Small Scale Wastewater Treatment Plants

Three wastewater treatment processes (oxidation ditch, extended aeration (plug flow type) and activated sludge batch reactor) which are considered to be suitable for small scale wastewater treatment plants were tested at a pilot plant, or using existing facilities to examine their methods of operation and maintenance. The objectives of this study were to determine production of excess sludge, a method of setting aeration intensity, and a method of controlling returned sludge.