Activated Sludge Basins Research Articles

Biological treatment of a pharmaceutical wastewater

The treatability of a pharmaceutical wastewater using a two-stage biological system was investigated. The system consisted of two reactors operated in a batchwise mode with the effluent of reactor A becoming the feed for reactor B. During a cycle of operation each reactor served, in turn, as the aeration basin and then clarifier. Reactor A was supplied with sufficient air to maintain good mixing of the reactor's mixed liquor. Attempts were made to keep the dissolved oxygen (DO) below 0.3 mg litre −1 and at hydraulic retention times (HRT) below 6.6 days the DO was 0 mg litre −1. Reactor B was operated under aerobic conditions during the REACT phase but DO levels dropped to 0 mg litre −1 during SETTLE when the reactor was most heavily loaded. Results indicated that a wastewater with a chemical oxygen demand (COD) and 5-day biological oxygen demand (BOD 5) of about 26 500 mg litre −1 and 12 500 mg litre −1 respectively could be treated with the system. COD removal by reactor A ranged from 96 to 63% while system COD removal ranged from 99 to 86% as various loading conditions were investigated. It was initially thought that the 2-ethylhexanoic acid present in the wastewater at a concentration of 2500 mg litre −1 might prove inhibitory to the biological process and adversely affect treatment performance. The system, however, adapted well and the 2-ethylhexanoic acid was effectively removed. Gas chromatographic analysis of reactor A's effluent suggested the occurrence of fermentation. Ethanoic, propanoic, butanoic and, on one occasion, pentanoic acids were detected. These were originally absent in the wastewater. The results suggested that the system might be further developed on the lines of the sequencing batch reactor (SBR) concept. In comparison to the conventional effluent treatment plant configuration comprising of trickling biofilters, activated sludge basins, secondary clarifiers and sludge return, the two-stage batch system would probably be simpler in terms of construction, operation and maintenance.

Oxygen Transfer Measurements and Air Distribution for an Aeration Basin with Fine Bubble Diffusers

The off-gas method was used to study oxygen transfer efficiency in a long, narrow activated sludge basin. The basin was equipped with square, ceramic, fine pore diffuser plates arranged in a uniform longitudinal pattern at a depth of 4.3 m. Oxygen transfer efficiency, at 20°C and zero dissolved oxygen concentration, during the second and third years following diffuser cleaning, was between 15 and 17%. A uniform distribution of air to the tank was compared with a tapered air supply (more air at the inlet end and less at the outlet). The tapered air supply gave lower dissolved oxygen at the outlet and did not increase overall oxygen transfer. With a 3 to 5-fold variation in air flow, at either the inlet or outlet zone of the basin, the oxygen transfer efficiency, adjusted for zero dissolved oxygen, stayed constant.

Use of monod kinetics on multi-stage bioreactors

At present, the alternatives of constructing either large units in biological waste water treatment plants (in this case single-stage activated sludge basins) or a few smaller units—either multi-stage reactors or reactors connected in series, is gaining more and more importance. In West Germany, in a recent workshop dedicated to this subject, it became evident that the knowledge of the significance of volume and/or sludge loads gained in decades of operating single-stage activated sludge tanks cannot readily be applied to multi-stage units. By extending the Monod reaction kinetics model for enzyme-substrate reactions a process analysis is carried out for a series-connection of up to four CSTR (completely stirred reactors) and the author presents a few graphical solutions to characterize and design a cascade-connected system.

A bacterial bioassay for assessment of wastewater toxicity

A bioassay using freeze-dried Nitrobacter as the test organism has been shown to successfully detect various toxicants in municipal and industrial wastewaters. The test is simple, sensitive, rapid and inexpensive; as a result, this test shows potential as a quantitative measurement technique for wastewater toxicity. The bioassay technique was applied in the analysis of a wastewater treatment system at a fiberboard plant near Portland, Oregon. The fiberboard is manufactured from a slurry of chipped wood, shavings and sawdust. Wastewater from the process is treated at an on-site facility consisting of settling ponds, activated sludge basin, clarifier and holding ponds. Treated water is recycled to the mill for reuse. Recently the removal of BOD by the activated sludge system dropped significantly and soluble and particulate organics began to accumulate. The influent and effluent flows for the treatment facility were tested with the Nitrobacter bioassay and both were determined to have significant toxicity. Further tests at points in the process showed that the toxicity was not associated with a single waste stream and was prevalent throughout the entire wastewater treatment system. In an effort to identify the toxicant, toxicity tests were conducted for known chemicals used in the process. The wastewater was treated with various physical and chemical unit processes to determine the most effective method for toxicity removal. Due to the complexity of the wastewater composition, no specific agents have been identified as solely responsible for the observed toxic response, however, several possible explanations for the apparent toxicity are discussed.

Long-Term Activated Sludge Treatment of Winery Waste Waters

Winery waste water, consisting primarily of clean-up water containing grape and wine residues, is being successfully treated by a long-term activated sludge treatment system. Retention time in the activated sludge basins ranges from 10 to 20 days. The system includes a screen, two activated sludge basins, clarifier, chlorination system, reaeration basin, sludge recycle and sludge digestion basin. Nutrients (anhydrous ammonia and phosphoric acid) are added to the influent. A polymer flocculant is added to enhance settleability of suspended solids in the clarifier. Characteristics of the treatment system influent and effluent are given, for both pressing (two months) and processing (10 months) seasons. System has achieved an efficiency of 99% in reduction of BOD₅. Nitrogen and phosphorus removal has exceeded 90%. Total suspended solids concentration in the effluent was less than 20 mg/l. Problems encountered in the operation of the system generally have been related to low temperature. Ice formation in the wintertime resulted in loss of biological activity in the activated sludge basins and equipment damage. Installation of a submerged turbine aeration system solved the wintertime aeration and mixing problems.

Long-Term Activated Sludge Treatment of Winery Waste Waters

Winery waste water, consisting primarily of clean-up water containing grape and wine residues, is being successfully treated by a long-term activated sludge treatment system. Retention time in the activated sludge basins ranges from 10 to 20 days. The system includes a screen, two activated sludge basins, clarifier, chlorination system, reaeration basin, sludge recycle and sludge digestion basin. Nutrients (anhydrous ammonia and phosphoric acid) are added to the influent. A polymer flocculant is added to enhance settleability of suspended solids in the clarifier. Characteristics of the treatment system influent and effluent are given, for both pressing (two months) and processing (10 months) seasons. System has achieved an efficiency of 99% in reduction of BOD₅. Nitrogen and phosphorus removal has exceeded 90%. Total suspended solids concentration in the effluent was less than 20 mg/l. Problems encountered in the operation of the system generally have been related to low temperature. Ice formation in the wintertime resulted in loss of biological activity in the activated sludge basins and equipment damage. Installation of a submerged turbine aeration system solved the wintertime aeration and mixing problems.

Die praktische Anwendung der elektrochemischen Sauerstoftbestimmung im Wasser

(1) The study deals with the electro-chemical measuring of oxygen contents in lakes and activated sludge basins according to the method ofTodt. The non recording short time test is used. (2) Exterior influences (conductivity, temperature, current, cathode surface) are discussed. (3) An oxygen sounder with good properties as regards mechanical strength and sensibility of the electrodes is described. (4) As further development, combined sounders called ‘Oxytester’ for measuring temperature and oxygen, respectively temperature, oxygen and conductivity were designed. (5) The disturbing influence of temperature on testing of oxygen is compensated electrically. (6) Tests with the oxytester in lake investigations reveal continuous profiles of oxygen, temperature and conductivity. In this way fine proportions of stratification can also be ascertained precisely. (7) The immediate diagrammatical representation of the tested values during the work on the lake gives precious indications for further testings. (8) Possibilities of measuring by sounders are illustrated by the test profiles from investigations made in some of the lakes in the Swiss Midland.