Performance comparison of activated sludge systems with conventional and extended aeration in removal of protozoan cysts and parasite egg from wastewater: a case study, Iran.
IntroductionDomestic wastewater reuse, as valuable sources of water for various purposes such as agriculture and irrigation, is one of the most important goals of wastewater treatment and protecting water resources especially in regions with scarcity of water resources (1, 2). However, reusing of wastewater, particularly in the term of agricultural and irrigation purposes, has several benefits, including: first benefits such as getting income from sale of treated effluent, reducing the amount of dust through the water spraying, utilizing nutrients such as phosphorus and nitrogen presented in wastewater, as a result, decreasing the chemical fertilizers utilization, and reducing the cost of tab water consumption. And Secondary benefits include the effects of wastewater re-use projects follow and public attention includes protecting the environment and improving the quality and appearance of water (3-5). Therefore, when wastewater is proposed to be reused in agricultural and irrigation, the control of microbiological contamination of effluent and its compliance with national and international standards will be more important (6, 7).
In reuse of wastewater, if health aspects and microbial quality of effluent are ignored, they will pose the serious risks to human health and environment, and also it is an important issue, whenever the treated effluent is intended to be used for irrigation of parks, food products and vegetables (8-10).Thus, it is suggested to treat wastewater based on parameters removal such as organic pollutants and pathogens in sewage. There are various treatment processes such as activated sludge, stabilization ponds, artificial wetlands, aerated lagoons and trickling filters that have been applied to treat raw wastewater (1).additionally, different mechanisms have been used for the removal of parasites egg during sewage treatment processes. The most particular mechanisms are precipitation and settling due to high density and weight, filtration, absorption by plant roots, trooping in the biological activated sludge clots and inactivation due to the unpleasant environmental conditions (2, 11, 12).
Many studies and investigations have shown that the percentage removal of parasites egg in trickling filter, aerated lagoon, activated sludge and both stabilization ponds and artificial wetlands have respectively reached to the level of 99%, 99.9%, 99%, 100%. Therefore, in each of these process and criteria the removal efficiency of parameters depends on wastewater characterization and treatment plants designed profile with lots of fluctuations (12, 15). Feachem et al., also revealed that the activated sludge process were capable to remove about 99% of parasite egg, (16), as well, Miranzade and Mahmodi showed that the activated sludge with extended aeration removed 100% of Nematode egg, It can be said that, the activated sludge systems are technologically appropriate solution for biological wastewater treatment systems (11).
According to the fewer research based on performance evaluation of wastewater treatment process in removal of protozoan cysts and parasite egg that have been studied in Iran and newly constructed of WTPs in Kermanshah province, the main objective of this study was evaluation and Comparison of Paveh, Sarpol-e-zahab (activated sludge with extended aeration) and Kermanshah (activated sludge with conventional aeration) WTPs in removing protozoan cysts and parasite egg and applying appropriate effluent of these systems for irrigation purposes.
Material and method
Samples of raw and treated Wastewater were taken at inlet (screening unit) in volume of 1 liter and outlet (after chlorination unit) in volume of 10 liters of each treatment plant (totally 24 equalized samples from each plant). The collected samples were composite samples taken over a period of 24 hours in randomize day of week as a method which described in standard method. The total 144 samples were collected through six months. Therefore, the analyzing of collected samples was carried out for parasitic egg according to the modified Bailenjer method with McMaster counting slide (with hole volume 3/0 ml) (17). Briefly, each sample was allowed to settle over 24 h in the laboratory at room temperature. Then, the supernatant was removed using siphon. Remaining sediment centrifuged at 1000x g for 15 min. And then, whole sediment of centrifuge tubes transfer to one centrifuge tube and centrifuge it again at 1000 x g for 15 min. after that, the pallet was suspended in equal volume of Stokes buffer (pH=4.5) and doubled volume of acetyl acetate were added, and sample was mixed entirely by stirring. The sample was then centrifuged at 1000 x g for 15 min. Three layers were taken place in all centrifuge tubes and then removed (upper black and middle layer).After that, sediment was suspended in five volume of zinc sulfate of 1.3(density 33%) and mixed thoroughly. This solution (precipitate + zinc sulfate) was considered as adequate volume of final product. Quickly, 0.3 ml was transferred to slide microscopic counting with a magnification of x 100 and x 40. The number of cysts and parasite egg were identified and counted. Following equation was used to calculate the number of cysts and eggs in samples obtained.
N = AX/PV
Where, N is the number of cysts or parasite egg per liter of sample, A the average number of eggs or cysts counted in three slides under microscopic observation, X the final volume of product in (ml), P the Volume put on the McMaster slide (0.3 ml), and the original sample Volume in (ml).
Data analysis
According to the lack of obtained normalize results (0.5<P), Statistical analysis using One-Samplekolmogorov Smirnov were performed to compare the data of effluent quality of two systems with significant level [alpha] = 0.05.And Statistical test of Mann-Whitney U were performed to compare the removal efficiency of Protozoan cysts and parasite eggs in two systems, using SPSS-Ver.11.5, with significant level [less than or equal to] 0.05.
Result
Results showed that the average removal efficiency of parasite eggs and protozoa cysts in Kermanshah treatment plant were respectively 97-99% and 99-100%. And for Paveh and Sarpol-e-Zahab treatment plants were respectively 97.5-100, 100; 99-100, 100%. There was statistically no significant differences between removal efficiency of all parameters in the effluent of all three WTPs (p>0.001).However, according to statistically test the average number of nematode parasite egg was less than the standard rate with significant differences (One-Samplekolmogorov test, p<0.001).
Table1 presents an overview of mean concentration of parasite eggs and protozoa cysts in raw and treated wastewater of all three WTPs, respectively. And also Table 2 reveals minimum and maximum rates of all parameters, respectively.
Discussion
This study provided identification and removal efficiency of parasite eggs and protozoa cysts in raw and treated wastewater of all three WTPs in Kermanshah province. Results of the samples analyses indicated that the average number of nematode egg is less than 1 number per litter (P<0.05). Consequently, With respect to effluents quality of all three WTPs and in comparison with the Iranian treated wastewater standards for agricultural irrigation has indicated that the effluent quality was in complied with the considered standards.
The removal efficiency of Kermanshah WTPs (activated sludge system with conventional aeration) facility for cysts and parasite egg have been estimated between 97-99% while the removal efficiency of Paveh and Sarpol-e-Zahab WTPs (activated sludge system with continuous aeration) were between 97.5-100%, so, there was no significant differences between all three WTPs in terms of statistical analyses, (P>0.05).But the performance of activated sludge system with extended aeration in removing cysts and parasite eggs were more than the activated sludge system with conventional aeration. This difference could be due to extended aeration time, and trapped or absorbed the parasite elements in the biological sludge mass and its separation in secondary sedimentation tank.
The results of recent study are consistent with similar reports. Feachem et al., have reported that the activated sludge process are capable to remove 99% of parasite eggs, (16).And also Miran Zadeh et al., showed that the activated sludge process with extended aeration, removing about 100 % of Nematode egg, (11). Donald, Rowe and Matteus et al, indicated that the primary sedimentation tank of activated sludge process with conventional aeration eliminates approximately 99% of the parasite egg, while the efficiency removal of 90% has been reported by Shuval et al (16). In addition, a secondary sedimentation tank in company with activated oxidation and oxygen ([O.sub.2]), can remove 94.5% of cysts, that is more than the activated sludge plus sedimentation tank with efficiency removal of 72.1-88%, Caccio et al (18). Also Casson et al., showed that the activated sludge systems are able to remove more than 99% of Giardia cysts (19), while, the efficiency removal of 99.5-99.8% has been reported by Wiandt, (20). A limitation include, lack of sampling during night time for collecting 24 hours composite samples was an example in this study.
In summarize, results obtained of this study demonstrated that the performance activated sludge system with extended aeration was more than the activated sludge system with Conventional in terms of parasites egg removal, but the performance of both treatment plants on elimination of parasite egg and protozoan cysts were desirable, meet the current agricultural guideline. However, effluent of these treatment plants can be considered for agricultural irrigation purposes with respect to considered standards. It is recommended to continue current operation and maintenance of these WTPs, with respect o agricultural standard (Engelberg indicator: number of Nematode egg per litter <1) the effluent of the system was desirable for agricultural purposes.
Acknowledgements
The authors wish to acknowledge the invaluable cooperating and supporting by Deputy of research committee of Kermanshah University of Medical Sciences, Health services of Kermanshah, Kermanshah wastewater company staff and officials of Kermanshah treatment plant for facilitating the issue of this project, with the No: 88091.
References
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Kiomars Sharafi (1), Meghdad Pirsaheb * (2) and Touba Khosravi (3)
(1) Lecturer of Environmental Health Engineering Department, Public Health School, Kermanshah University of Medical Sciences
* (2) Correspondent Author: Associated Professor of Environmental Health Engineering Department, Member of Research Center Kermanshah University of Medical Sciences, Public Health School, Kermanshah University of Medical Sciences.
(3) Environmental Engineering Department, Public Health School, Kermanshah University of Medical Sciences, Kermanshah, Iran
* Corresponding Author E-mail: mpirsaheb@yahoo.com.
Table 1: Mean concentration of parasitic pollution in raw and treated wastewater in all three WTP (Number per liter) plant name sampling Ascaris Hymenolepis Trichuris Place lumbricoides nana egg trichuria egg Kermanshah Influent 45.75 4.52 0 Effluent 0.97 0 0 Sarpol -e- Influent 45.85 5.07 2.49 Zahab Effluent 0.45 0 0 Paveh Influent 38.88 6.84 0 Effluent 0.56 0.11 0 plant name sampling Giardia Amibia Total Place cyst cyst parasite egg Kermanshah Influent 10.77 19.33 50.27 Effluent 0.35 0.22 0.97 Sarpol -e- Influent 14.44 7.49 53.41 Zahab Effluent 0.24 0 0.45 Paveh Influent 15.55 9.87 45.72 Effluent 0.2 0 0.67 plant name sampling Memathoda Parasitic Place parasite cyst egg Kermanshah Influent 45.75 30.1 Effluent 0.97 0.57 Sarpol -e- Influent 48.34 21.93 Zahab Effluent 0.45 0.24 Paveh Influent 38.88 25.42 Effluent 0.56 0.2 Table 2: Minimum and maximum number of parasite eggs and protozoa cysts in raw and treated wastewater in all three WTP (number per liter) plant name sampling * Min/Max Ascaris Hymenolepis Place Number lumbricoides nana egg egg Kermanshah Influent Min 0 0 Max 175 50 Effluent Min 0 0 Max 4 0 Sarpol Influent Min 6 0 -e- Zahab Max 120 33.2 Effluent Min 0 0 Max 2.7 0 Paveh Influent Min 6.7 0 Max 80 33.3 Effluent Min 0 0 Max 3 2 plant name sampling * Min/Max Trichuris Giardia Amibia Place Number trichuria cyst cyst egg Kermanshah Influent Min 0 0 0 Max 0 40 93.3 Effluent Min 0 0 0 Max 0 2 3.2 Sarpol Influent Min 0 0 0 -e- Zahab Max 18.3 0.7 90 Effluent Min 0 0 0 Max 0 1 0 Paveh Influent Min 0 0 0 Max 0 82 65 Effluent Min 0 0 0 Max 0 2 0 plant name sampling * Min/Max Total Memathoda Parasitic Place Number parasite parasite cyst egg egg Kermanshah Influent Min 0 0 0 Max 225 175 105.7 Effluent Min 0 0 0 Max 4 4 3.2 Sarpol Influent Min 6 6 0 -e- Zahab Max 120 120 120 Effluent Min 0 0 0 Max 2.7 2.7 2.3 Paveh Influent Min 6.7 6.7 0 Max 83.3 80 82 Effluent Min 0 0 0 Max 3 3 2 * Min/Max: Minimum and maximum number of parasite eggs and protozoa cysts in raw and treated wastewater.
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