The performance of selector to solving bulking sludge problem in activated sludge process

Transcription

1 The performance of selector to solving bulking sludge problem in activated sludge process A. Mohseni-Bandpi & Z. Yousefi Department of Environmental Health Engineering, Health Faculty, Sari, Iran. Abstract An investigation was carried out to evaluate the performance of selector in activated sludge under extended aeration mode to control bullung sludge problem. The first phase of this study a bench scale of extended aeration process without a selector was run to evaluate the possible formation of bulking sludge. The results of this part show that SVI value was dg. After using hydrochloride powder as a chemical material for controlling bullung sludge problem, the SVI reduced to 50 to 80 mllg. After installing a selector zone this value was corrected to 80 to 120 d g. The second phase of this research, a pilot scale extended aeration process was designed and constructed with plastic material and a selector was installed in head of aeration unit. The characteristics of the pilot scale reactor were 1200, 140 and 70 liter volume for aeration tank, settling tank and selector respectively. The results of this part revealed that the SVI value, Turbidity and COD removal efficiency were dg, 1.4 to 5 NTU and 90 to 98% respectively. The results also showed that during the research study no bulking sludge problem was observed from the pilot reactor. It may be concluded that, the selector is the best alternative, cost effective and more practicable method to controlling the bulking sludge problem in the activated sludge treatment plant system. Introduction Sewage systems are effective for improving river water quality in terms of reduction of discharged pollutants, however, there is a limit ability to control

2 discharge of pollutants into the rivers due to some problems in traditional small wastewater treatment. Mazandaran province placed in the North of Iran. Sari City is its center. This province concerned with many rivers that flowing to the Caspian Sea. Distances of the rural community and small cities in these areas are very less. Unfortunately lack of sewerage system (sewers) in all of these areas are cause of polluted rivers. Gray water and leachate and septic tank effluent and miscellanies effluent discharge to the rivers. Septic tank, Aqua-privies and latrines are traditional sewage treatment in these small communities that are unable to prevention of water pollution and need to change or modify by a supplementary wastewater treatment. Authorities of the areas follow up the ways to prevent water pollution by On-site wastewater treatment. The condition of watercourse in these areas is unpleasant and really need to emergent solving procedures. Water and wastewater management systems follow up the best way to protection of these rivers and watercourses and are chatting to scientific centers for research and indicate the best available technology for small communities' wastewater treatment. Unfortunately most of traditional extended aeration package plant due to existence problems such as bulking and rising sludge is not popular acceptable. In recent years the process of upgrading wastewater treatment facilities all over the world Jurg and Rene (1). Activated sludge is today the most commonly used process in wastewater treatment Michael et a1 (2). Most activated sludge plants around the world suffer from bulking sludge Krisna et a1 (3) and Linda et a1 (4). Bulking sludge in secondary tanks is a serious problem. One of the important reasons of bulking sludge is due to excessive growth of filamentous microorganism. The low FIM another important reason of bulking sludge is not clear. Pujol and Canler (5) reported that the low FIM bulking phenomena were avoided by contact zones (selector), but Casey et a1 (6), and Eikelboom (7) did not observe an improvement in the settling properties of low F/M bulking sludge offer installing selectors.. Low FIM bulking cannot be avoided by small anoxic selectors, but large anoxic selectors are necessary, causing "complete" denitrification in the anoxic zone. This study has already been recommended by casey et a1 (8) in order to prevent low FIM bulking. In Iran the most commonly wastewater treatment plants for small community such as industrial, commercial and institutional area, domestically apartment even individual homes is activated sludge under extended aeration modification process. Abundance problem of these plants is bulking sludge phenomena that can be effected on the efficiency of the plants which breakdown the objectives of work. So, The main objectives of this research were, to optimization of a traditional system to prevention of water pollution and improve of water quality. In addition to effectiveness of selector in controlling bulking sludge, and the effect of different process conditions on the overall pollution removal capability of the treatment system also was studied.

3 Materials and Methods Water ~ol/zrtion 1'1 179 Bench-Scale The bench-scale activated sludge system under extended aeration mode was used to removal pollution without selector. It was made of glass material. Acvarium Pump and diffuser stones supplied air to aeration tank. Sludge was recycled to aeration tank by airlift. Pilot- Scale The package pilot plant activated sludge system under extended aeration mode was design to evaluate the selector performance. A selector zone was installed ahead of aeration tank to controlling bulking sludge problem. It was made of plastics. Air was supplied to the system by a compressor. The characteristics of the bench and pilot scale reactors are shown in Table 1. Table 1. The characteristics of bench and pilot scale reactors Parameters I Volume of aeration tank Volume of settling tank Volume of Selector Liter Unit I Liter Liter Bench- Scale Pilot-scale 1200 Analytical Methods BOD, COD, TSS, OUR and Turbidity were analyzed according to Standard Methods (1992). Settleability of sludge was measured as Sludge Volume Index, SVI (mug). Raw wastewater quality The wastewater investigated in this study was obtained from 600 hundred residential apartments sewerage collection system. The characteristics of the raw wastewater are summarized in Table 2. Table 2. The characteristics of raw wastewater quality Parameters COD BOD TSS TKN Total P Cn~t mg l Range of concentration

4 Results and discussions Controlling Bulking Sludge In order the evaluate the performance of bench scale and pilot scale for controlling of bulking sludge, initially the bench scale was run without selector. The results of both reactors to controlling bulking sludge are shown in Figure 1. As shown in Figure 1. When initially bench scale was run without selector, the SVI was in the range of during 7 weeks and this value was reduced when chlorinated powder was used to controlling bulking sludge during between 8-18 weeks. The SVI value again rises after 18th weeks in bench scale reactor (Figure 1). Then a selector zone was installed in bench scale and its effectiveness on the solving bulking sludge problem is shown in Figure 1 during weeks. The performance of pilot scale reactor to controlling bulking sludge also is shown in Figure l. The SVI value was around d g in pilot scale reactor. T-X - l Pdot-Scale 1 -m - Bench-Scale, 7 1 Figure 1. The effect of selector on the SVI value in both reactors Oxygen uptake rate (OUR) The in both reactors are shown in Figure 2. As shown from Figure 2 in the bench scale reactor due to dominant of filamentous bacteria, the was low, while in the pilot scale due to dominant floc forming bacteria, the was very high. As shown from Figure 2 after 30 minutes the value of dissolved oxygen was decreased to zero in pilot reactor.

5 Interface of Sludge (Settleability of sludge) The settleability of sludge in both reactors is shown in Figure 3. As shown in Figure 3 in bench scale reactor after 30 minutes the interface line just decreased from 1000 to 940 ml, while this value in pilot reactor decreased from 1000 to 200 ml. This confirmed that due to bulk condition poor settleability sludge was observed in bench scale reactor Tune (mm) l I l Figure 2. The OUR versus time in both reactors X- X-X- X- x- X-X-, -P~lot-Scale -X- Bench-Scale, Bulkmg Cond~t~on Tune (mm) Figure 3. The sludge interface height versus time in both reactors --L

6 l 82 Water ~oll~rtion 1.1 TSS in the effluent The effluent of TSS in both reactors is shown in Figure 4. The Figure 4 is shown that due to bulking problem in bench reactor the TSS was higher than pilot reactor. - Time (Weeks) Figure 4. TSS in the final effluent in both reactors COD removal efficiency The COD removal efficiencies in both reactors are summarized in Table 3. From Table 3 during the first 7 weeks due to bulk condition in bench reactor, the COD removal efficiency were %. The COD removal efficiency was increased between 8 to 18 weeks in bench scale, when hydrochloride was used as a chemical material for controlling of bulking sludge. The COD removal efficiency again decreased after 18th weeks. The COD removal efficiency in pilot scale was almost more than 90%.

7 Table 3. COD removal efficiencies in both reactors CODs (Eff) 3ench Pilot 63 49

8 Conclusion This research study investigated the possibility of using selector for controlling bulking sludge in activated sludge process. The SVI value were and mug for reactor without selector and with selector respectively. The COD removal efficiency was approximately and 90-98% for bulk and non-bulk conditions. The results indicted that due to poor settleability sludge in bulk condition high TSS was found in the final effluent. It can be concluded that the selector is the best alternative, cost effective and more practicable method for controlling bulking sludge problem in the activated sludge treatment plant systems. References 1. Jurg, K & Rene, B. Low FIM bulking and scumrning, towards a better understanding by modeling, Wat. Sci. Tech. 31, pp , Michael, R. R, Torben, L, & Frederic, C. Improving settling dynamics of activated sludge by adding fine Talc powder. Wat. Sci. Tech. 34, pp , Krisna, R. P,, David, J., Wendell, H. K. Nocardia control in activated sludge by classifying selectors. Water Env. Res., 64, pp Linda, L. B, Ellizabeth, M. S, Debbie, B & Robert, J. S. Towards understanding the taxonomy of some of the filamentous bacteria causing bulking and foaming in activated sludge plants. Wat. Sci. Tech. 34, pp , Pujol, R. and Canler, J. P. Contact Zone: French practice with low F/M bulking control. Wat. Sci. Tech. 29, pp Casey, T. G., Ekama, G. A., Wentzel, M. C. and Marais, G. V. R. Cause and control of filamentous bulking in nutrient removal activated sludge system. IAWPRC workshop on prevention and control of bulking activated sludge, Perugia, June Eikelboom, D. H. The Microthrix parvicella puzzle. Wat. Sci. Tech. 29, pp Casey, T. G., Wentzel, M. C., Ekama, R. E., Loewenthal, R. E., & Marais G. V. R. A hypothesis for the cause and control of anoxic-aerobic filament bulking in nutrient removal activated sludge system. Wat. Sci. Tech. 29. pp