Microbiological and Biological Aspects of the Wastewater Treatment Plant Wschód in Gdańsk - PDF

Polish Journal of Environmental Studies Vol. 12, No. 6 (2003), Microbiological and Biological Aspects of the Wastewater Treatment Plant Wschód in Gdańsk K. Olańczuk-Neyman*, M. Geneja, B. Quant,

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Polish Journal of Environmental Studies Vol. 12, No. 6 (2003), Microbiological and Biological Aspects of the Wastewater Treatment Plant Wschód in Gdańsk K. Olańczuk-Neyman*, M. Geneja, B. Quant, M. Dembińska, K. Kruczalak, E. Kulbat, I. Kulik-Kuziemska, S. Mikołajski 1, M. Gielert 1 Hydro- and Environmental Engineering Faculty, Gdańsk Technical University, G. Narutowicza 11/12, Gdańsk, Poland 1 Saur Neptun, Gdańsk Received: 5 March, 2003 Accepted: 30 April, 2003 Abstract This study indicates that in the wastewater treatment plant Wschód in Gdańsk, working in the modified UCT system, the effectiveness of bacteria pollutant removal varies from 92 to 99% and almost 100% of parasites are removed. Despite this, the number of indicator bacteria and periodical presence of Salmonella in the effluent indicates that it is strongly bacteriologically polluted. It was discovered that the number of indicator bacteria in primary sludge was by 1 to 3 orders of magnitude higher than in the excess activated sludge. Also, Salmonella was twice more frequently detected in the primary sludge than in excess activated sludge (70% and 30%, respectively). In contrast, the average number of invading helminths ova (ATT) was over two times higher in excess activated sludge than in primary sludge. An efficient method for controlling activated sludge bulking resulting from intensive growth of Microthrix parvicella was dosing of PAX-16 (the doses from 2.5 to 4.8 g Al 3+ /kg d.m. d). Keywords: activated sludge, modified UCT system, removal of bacteria and parasites, filamentous bacteria *Corresponding author Introduction Since the operation of Polish wastewater treatment plants (WWTPs) with multiphase activated sludge systems for integrated removal of organic carbon, nitrogen and phosphorus started only a few years ago, a number of operational problems have still not been fully elucidated. For instance, the data concerning the effectiveness of elimination of bacteria and parasites as well as biological characteristics of activated sludge and the reasons for periodical intensive growth of filamentous bacteria, are scarce. Also, sludge bulking due to periodical filamentous growth, resulting in foams and scum formation on the surface of bioreactors and deterioration of effluent quality, is not explained well, although it seems to be one of the most serious operational problems of multiphase, lowrate sludge systems [1, 2, 3, 4]. This paper presents the results of investigations concerning the biological aspects of operation of the modern WWTP Wschód in Gdańsk, where a multiphase activated sludge system co-operating with a unit for VFA generation from primary sludge is working. The investigations were carried out during the first two years of operation of the WWTP ( ), in close co-operation with the operator of the facility, company Saur Neptun Gdańsk. 748 The Study Area The wastewater treatment plant Wschód in Gdańsk underwent upgrading and modernization in the years The plant receives about 90,000 m 3 of sewage per day. Mechanical treatment units consist of mechanical screens, aerated sand traps with grease removal traps and radial-flow primary sedimentation tanks. Biological treatment units consist of 6 multiphase MUCT (modified UCT system) reactors and 12 radial-flow secondary sedimentation tanks. A typical MUCT system was additionally equipped with a transitional chamber which can optionally serve as a nitrification or denitrification chamber and with deaeration chamber, where the mixture of treated wastewater and activated sludge, recirculated from nitrification chamber to denitrification chamber, is de-oxidized. The plant is equipped with a three-chamber fermenter with complete mixing, co-operating with primary sedimentation tanks. Pre-fermented sludge, containing volatile fatty acids (VFAs), is discharged to sewage before primary sedimentation tanks. Thanks to this, sewage before biological treatment becomes enriched with organic substances, necessary for effective biological dephosphatation. Since 2002 the treated sewage is transported via a pipeline into the Bay of Gdańsk and discharged 2.3 km away from the coastline. In the period from 2000 to 2001 a two-year investigation of sewage and one-year investigation of sewage sludge were carried out. The samples were collected 1-2 times a month. Altogether 114 samples of sewage and 19 Olańczuk-Neyman K. et al. samples of sludge were collected. The samples of sewage were collected at the following sampling points (Fig. 1): after screens (sampling point no. 1), after primary sedimentation tanks (sampling point no. 2) and from the effluent (sampling point no. 3). The grab samples of raw sewage were collected at 9:00 a.m., the samples of mechanically treated sewage - at 11:00 a.m. and the samples of biologically treated sewage - at 10:30 a.m. next day. The mean samples were acquired by mixing the three grab samples collected at 5-minute intervals. The samples of sludge were collected from primary sedimentation tanks (sampling point no. 4) and raw excess sludge from secondary sedimentation tanks (sampling point no. 5). The samples of activated sludge for microscope analysis were collected once a month from the beginning and the final section of the nitrification chamber, from the aerobic, anoxic and deaeration chambers and from external activated sludge recirculation pipeline. The samples were transported to the laboratory in a portable refrigerator and analyzed immediately. Methods Bacteria The basic microbiological analyses included determinations of the following types of bacteria: the coliform bacteria, E.coli, faecal enterococci and Clostridium perfringens. The extended analyses also included determinations of Salmonella. The standard dilution method was used for determination of indicator bacteria (using from seven to ten dilutions) and standard membrane filters method. Bacteria were plated onto the following culture media: the coliform Fig. 1. Location of sewage and sludge sampling points. 1 - raw sewage (after screens, 2 mechanically treated sewage, 3 biologically treated sewage (after MUCT reactors and secondary sedimentation tanks), 4 primary sludge, 5 waste activated sludge (WAS), 6 activated sludge from bioreactor. Microbiological and Biological Aspects of the Wastewater Treatment bacteria and E.coli on the Fluorocult LMX broth medium with MUG substrate (according to Elmund et. al. [5]), presence of suspected E. coli was indicated by fluorescence in the UV rays and positive indol reaction, enterococci on Chromocult medium Enterococci broth and Cl. perfringens on TSC medium. All nutrient media were produced by Merck. The results of investigations were presented as MPN in 100 cm 3 of sewage or sludge. The prevalence of Salmonella was detected according to the following schedule. The 1 dm 3 of sewage was centrifugated (4000 r.p.m) and obtained supernatant was filtered on a membrane filter with pores of 0.45 μm diameter. The membrane filters and the sediment left after centrifugation were used in further analyses. In the case of sewage sludge the 10 ml of sewage sludge samples were used. The samples were inoculated into the liquid selective-multiplication medium with acid sodium selenite (SF). The cultures were incubated at 37 0 C for 24 hours and then plated onto the following agars: weaklyselective MacConkey (MC) and two strongly-selective: Salmonella-Shigella (SS) and Wilson-Blair (WB) produced by Becton-Dickinson. Identification analyses were carried out using API 20 E tests, followed by serotyping. Identification analyses were performed in microbiological laboratory of Isolation Hospital in Gdańsk. The number per 1 dm 3 of sewage and per 1 kg of d.m. of sludge were obtained after recalculation. Helmints The analyses of prevalence of Ascaris sp. and Trichuris sp. ova were carried out according to the method described by Wasilkowa (The guidelines of Health Department [6]). For analysis of prevalence of Toxocara sp. ova, flotation method described by Quin et al. (Gundłach et al. [7]) was used. Results were given as the number of parasites ova per dm 3 of sewage and per 1 kg of d.m. of sludge. Altogether 59, samples of sewage and 12 samples of sludge were analyzed. Activated Sludge The basic biological investigations of activated sludge consisted of evaluation of composition of activated sludge in the multiphase bioreactor. Biocenosis fluctuations in the nitrification zone was especially analysed. The qualitative evaluation of bacteria in the samples of activated sludge was performed on the basis of microscope observations. Bacteria were divided into three basic groups: 1. cylindrical (rod-shaped), dispersed free swimming, 2. filamentous, 3. zoogleal and cocci. The following features are characteristic of filamentous bacteria: shape and length of filaments (straight, curved, long, short), presence of sheath, formation of whirls and bands, filaments stuck in flocs, filaments with real or false branches. Identification of filamentous bacteria was performed by means of microscope observations of prepared slides stained with Gram method and Nessier method [8] at magnification x400 and x600. The bacteria of genus Spirillum and Spirochaeta were identified on the basis of motion. Three-stages scale was used in evaluation of activated sludge bacteria: x - rare (single cylindrical, filamentous or zoogleal bacteria in some microscopic fields), xx - common (several tens of rod-shaped bacteria, a dozen of filaments or a few zooglea in a microscopic field), xxx - numerous (several hundred rods, several tens of filaments or a dozen zooglea in a microscopic field). The qualitative analysis of activated sludge microfauna using microscopic magnification from x170 to x680 was performed. The bulking phenomenon was evaluated on the basis of sludge volumetric index (SVI) and diluted sludge volumetric index (DSVI). Intensity of activated sludge foaming in bioreactors was evaluated visually - by estimating the percentage of a bioreactor s surface covered with foam and scum. Physical and Chemical Analysis In March 2002 investigations concerning the effectiveness of control of intensive filamentous bacteria growth by means of polialuminium chloride (PAX-16 produced by Kemipol) and ferric sulfate (PIX-113, produced by Kemipol) were performed. An existing installation for chemical precipitation of phosphorus was used for dosing the reagents to the outflow from nitrification chambers of the bioreactors. PAX-16 was introduced to bioreactor no. 4, where the most intensive foaming occurred and the layer of scum was the thickest. For 8 days the dose from 2.5 g Al 3+ / kg d.m. d to 4.8 g Al 3+ /kg d.m. d and for the next 9 days the dose from 1.70 to 2.11 g Al 3+ /kg d.m. d were introduced to the reactor. PIX-113 was dosed to bioreactor no. 5, in the amount from 6.5 to 9.3 g Fe/kg d.m. d. In grab samples of sewage outflowing from the secondary sedimentation tanks the values of COD and BOD 5 and concentrations of TSS, TN, NH 4 -N, NO 3 -N and TP were determined. The measurements were carried out according to the Polish Standards for water and wastewater: TSS (PN-72 C-04559/02), nitrates (PN-82 C-04576/08). Measurements of COD, total nitrogen, ammonia nitrogen and total phosphorus were carried out using the microanalitical methods of Merck company, spectrophotometer S12 and mineralizer CR3000 produced by WTW. BOD 5 was measured manometrically using OxiTop apparatus produced by WTW. Results Bacteriological Analyses Sewage The results of determinations of the most probable number (MPN) of indicator bacteria: coliforms, faecal coli (suspected E.coli), faecal enterococci and Clostridium per- fringens in raw sewage, mechanically treated sewage and in the effluent are presented in Figs. 2, 3, 4 and 5. 750 Olańczuk-Neyman K. et al. In raw sewage the average geometrical values were as follows: coliforms (7,48 log 10 ), E.coli (7.04 log 10 ), faecal enterococci (6.36 log 10 ), Clostridium perfringens (7.04 log 10 ). The number of indicator bacteria (min-max) varied in range from about 2 log 10 (coliform bacteria 2 log 10, E.coli 2.24 log 10, faecal enterococci 2.36 log 10 ) to about 3.00 log 10 (Clostridium perfringens). In mechanically treated sewage the number of indicator bacteria (MPN) was similar to the MPN in raw sewage; however, the range of fluctuations was higher, from about 2.1 log 10 for coliform bacteria and E.coli, 2.25 log 10 for faecal enterococci to 4.7 log 10 for Clostridium perfringens. Temperature of sewage was found to affect the number of E.coli. The highest numbers of E.coli were detected in the periods when temperature of sewage was above 18 0 C (from May to October 2000 and 2001). In the effluent from the WWTP, the fluctuations of number of indicator bacteria varied from approximately 1.5 log 10 for Clostridium perfringens to about 2.5 log 10 for other bacteria. Neither seasonal changes resulting from sewage temperature, nor effect of variable loading of activated sludge (from to kg BOD 5 /kg d ) on the MPN of analyzed indicator bacteria was discovered. Usually the geometrical average number of indicator bacteria in treated sewage was by about 2 orders of magnitude lower than in raw sewage. In sewage inflowing to the WWTP, the Salmonella bacteria (in 1 l) were present in 22.7% of analyzed samples. In 2001 Salmonella was more frequently detected (33% of samples) than in 2000 (10% of samples). Salmonella was detected in 5% of analyzed samples of treated sewage. The following species occurred most frequently: S. thompson, S. virchow, S. dublin, S. infantis and S. from serological group C1 (Table 1). All serotypes listed above are capable of causing food poisoning in humans. Fig. 2. The MPN of coliform bacteria in raw sewage, mechanically treated sewage and effluent from the WWTP. Fig. 4. The MPN of faecal enterococci in raw sewage, mechanically treated sewage and effluent from the WWTP. Fig. 3. The MPN of probable E.coli bacteria in raw sewage, mechanically treated sewage and effluent from the WWTP. Fig. 5. The MPN of Clostridium perfringens in raw sewage, mechanically treated sewage and effluent from the WWTP. Microbiological and Biological Aspects of the Wastewater Treatment Table 1. The species of Salmonella isolated from sewage and sewage sludge of the WWTP Wschód in Gdańsk. No. Bacteria Sewage Sludge Raw Treated Primary Excess 1. S. virchow x x x x 2. S. thompson x x 3. S. gr. serolog. B x x 4. S. gr. serolog. C1 x x 5. S. infantis x 6. S. dublin x 7. S. livingstone x 8. S. gr serolog. D x 9. S. typhimurium x 10. S. hadar x 11. S. enteritidis x Sludge The number of indicator bacteria in primary sludge was substantially higher than in waste activated sludge. The geometrical mean (GA) of coliform bacteria and suspected E. coli in primary sludge reached 6.0x10 7 and 4.6x10 7 /100 ml, respectively, and was by about an order of magnitude higher than in excess sludge. The GA number of faecal enterococci (2.1x10 7 /100 ml) was by almost 2 orders of magnitude higher and the number of Clostridium perfringens (4.3x10 5 /100 ml) was by more than 3 orders of magnitude higher in primary sludge [9]. Salmonella was isolated from 70% of primary sludge samples (S. virchow, S. from serological group B, S. typhimurium, S. hadar, S. from serological group D. and S. enteritidis) and 33% samples of excess activated sludge samples (S. livingstone, S. thompson, S. virchow, S. from serological groups B and C1) (Table 1). Parasitological Analyses Sewage Raw sewage contained the highest number of Ascaris sp. parasites - between 0 and 8 active (invading) ova in 1 L and from 0 to 5 passive (non-invading) ova in 1 l. The content of parasitic ova in mechanically-treated sewage was significantly lower - from 0 to 2 per 1 L of active ova and from 0 to 1 per 1 l of passive ova. No Trichuris sp. ova were detected during the entire investigation period. Sludge The mean number of viable Ascaris sp., Trichuris sp. and Toxocara sp. ova in primary sludge was 533, 267 and 233/kg d.m. and 2167, 500 and 0/kg d.m. in waste-activated sludge. Only on rare occasions were the helminths ova not detected in sludge samples (i.e. in October 2001). Biological Investigations of Activated Sludge In the aerobic zone of bioreactor (nitrification chamber) zoogleal bacteria dominated. Additionally, mostly in the beginning part of this chamber, small filamentous bacteria growing out of flocs were found. The number of filamentous bacteria substantially increased in the periods of low temperature (January, February, November). Only occasionally single Spirillae and Spirochetae as well as free-swimming rod-shaped bacteria were present. 19 species of sedentary ciliates were detected. The dominant ciliate species was Epistylis plicatilis (from 360 to 2380 per ml), the subdominant was Vorticella sp. (from 200 to 680 per ml) and occasionally found genera were Opercularia and Zoothamnium. Among crawling ciliates, the most numerous species was Aspidisca costata (from 40 to 1880 per ml). The greatest number of this ciliate were found in the beginning part of the chamber. Two genera, of free swimming ciliata, Euplotes and Linotus were detected outside the periods of low temperature (from 40 to 120 per ml). Relatively low numbers of sporozoa and colourless flagellates were observed: Cochliopodium granulatum from 120 to 640 per ml, Arcella vulgaris from 80 to 560 per ml and the Amoeba sp. - from 40 to 240 per ml. In low temperature periods neither quantitative nor qualitative changes in this group were noted. The Rotatoria numbers were low (from 20 to 60 per ml). In the anaerobic zone (the phosphates releasing), opposite as in the aerobic zone, zoogleal bacteria were scarce. The free swimming rod-shaped bacteria and various types/ genera of filamentous bacteria dominated. From several 752 Fig. 6. The doses of PAX-16 (g Al 3+ per 1 kg MLSS per day) applied in the subsequent days of experiment. tens to several hundreds per ml of sporozoa and colourless flagellates as well as single crawling ciliate from the Aspidisca costata a were also observed. In the anoxic zones (denitrification), the number of filamentous bacteria was smaller than in the anaerobic chambers and also fewer types of these bacteria were detected. The sporozoans were more numerous than colourless flagellates. The number of ciliates, which was very low in the I denitrification zone (1 free swimming, 2 crawling and 3 sessile species from the Vorticella genus), increased in the II denitrification zone (5 species of free swimming ciliates, 2 crawling and 7 sessile species). A high number of ciliates was detected in the deaeration chamber: sessile Epistilis plicatilis (to 3000 per ml) and crawling Aspidisca costata (about 900 per ml). Control of Activated Sludge Bulking and Foaming Using Chemical Methods Olańczuk-Neyman K. et al. Problems with activated sludge bulking and foam and scum formation in bioreactors have occurred during periods of low temperature since 1998, but in winter season 2001/2002 especially intensive filamentous growth took place. The foams and scum of floating sludge gathered on the surface of bioreactor s chambers - especially of the nitrification chamber. The floating layer of activated sludge outflowed with wastewater from secondary sedimentation tanks, causing substantial deterioration of the quality of effluent from the WWTP. The concentration of total nitrogen increased by 30% and values of COD, BOD 5 and concentrations of TSS and total phosphorus increased 2-3 times. During winter (2002), investigations of samples of scum of floating sludge from aerobic and anaerobic chambers of bioreactor were performed. A great number of filamentous bacteria was detected in the collected samples. The prevalence of filamentous bacteria both in aerobic and anaerobic chambers of bioreactor indicated that they belong to the A group of microorganisms according to Eikelboom and van Buijsen [8
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