Feasibility Study of Lime Addition Method for Biosolids Stabilization in West Ahwaz Wastewater Treatment Plant

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1 Feasibility Study of Lime Addition Method for Biosolids Stabilization in West Ahwaz Wastewater Treatment Plant M. Farzadkia*, N. Jaafarzadeh*and L. Loveimi Asl* * Department of Environmental Engineering, Islamic Azad University, P.G. Studies and Research Center, Ahwaz, Iran. (E- mail: mehdi_farzadkia@yahoo.com) Abstract: Disposal biosolids from west Ahwaz wastewater treatment plant (WWTP) usually was used for agricultural activities. Initial evidence showed that these biosolids were untreated therefore; it could transmitted many pollutants to environment and created many hazards for public health. Anaerobic digester was choosing for this WWTP. The main objectives of this research is evaluated the reuse potential of disposal biosolids from anaerobic digester, and determine the efficiency of lime addition method for these biosolids stabilization. This study was conducted over 12 months from July 2005 to June In each stage, the samples of disposal biosolids from digester and lime addition reactor were taken and analyzed for evaluation of stabilization and reuse potential. Lime addition of biosolids was performed in the reactor with 30-liter capacity at the west Ahwaz WWTP. Averge amounts of fecal coliform and viable helminthes ova densities in disposal biosolids from west Ahwaz WWTP were MPN per gram of dry solids and 314 ova per 4gram of dry solids, respectively. By lime addition ratio about gram Ca(OH)2 per gram of dry solids of biosolids, ph was not dropped under 12, and fecal coliform was not growth after 30 days. Discharge biosolids from west Ahwaz WWTP was raw and very dangerous for reuse or disposal. Lime addition could be stabilized these biosolids and also reduced fecal coliforms more than 99.99% and obtained class B of USEPA criteria. Lime stabilized biosolids could be well used for reconditioning the poor soil and or, for covering of solid waste landfill-site. Keywords: Biosolids Stabilization; Lime Addition; Reuse INTRODUCTION At the present time, there are not any principle pollution control activities on the disposal biosolids from wastewater treatment plants in Iran. Therefore, disposal biosolids usually was raw. If it will be reused or discharged to the environment, many hazardous materials would be polluted natural resources such as water, soil and agricultural products. Unfortunately, there is not any data from the relationship between this type of pollution and health hazards in Iran (Venglovsky, 2002). A little researches that were done by Farzadkia (Farzadkia, 2002) in four wastewater treatment plants in Tehran showed that the disposal biosolids from these plants were raw and could not be disposed to the environment. Due to this regards, investigation on quality of disposal biosolids from Ahwaz wastewater treatment plant (WWTP) was considered. At the present time, there is only one wastewater treatment plant in Ahwaz city. This plant worked based on the activated sludge process for wastewater treating and anaerobic digesting for biosolids stabilization. Usually, effluent and disposal biosolids from this plant are used for agricultural activities. Two stages anaerobic digester was used in this WWTP. Due to the first stage of digester was damaged and out of services, disposal biosolids from this WWTP would be raw. The main objectives of this research are: 1) evaluated on the stabilization degree of disposal biosolids, 2) study of the lime addition process for these biosolids stabilization. 1129

2 Lime stabilization Lime stabilization is generally more cost-effective and simpler than alternative biosolids options and quality of the resultant biosolids is often superior. These plants may be easily added to processes that have inadequate capacity to meet regulatory requirements. In this process, lime is added to untreated biosolids in sufficient quantity to raise the ph. The lime dosage required varies with the type of biosolids and solids concentration. Typical dosages are reported in table 1 (Metcalf, 2003). The high ph creates an environment that halts or substantially retards the microbial reactions that can otherwise lead to odor production and vector attraction. The biosolids will not putrefy, create odors, or pose a health hazard so long as the ph is maintained at this level. The process can also inactivated virus, bacteria, and other microorganisms present (Bruce, 1984). Table 1: Typical lime dosages for pretreatment sludge stabilization Most lime treatment facilities have the flexibility to produce either class A or class B regulations recommended by united state environmental protection agency (USEPA) (USEPA, 1993). To meet Class B requirements using lime stabilization, the ph of the biosolids must be elevated to more than 12 for 2 hours and subsequently maintained at more than 11.5 for 22 hours. To meet Class A, the Class B elevated ph requirements are combined with elevated temperatures (70ºC for 30 minutes) (Lue-Hing, 1998). Based on the classes of lime-stabilized biosolids achievement, which could be reused as a solid waste landfill cover, commercial fertilizer or soil conditioner (USEPA, 2000) According to the water environment federation (WEF), as of 1997 in the USA, almost 20 percent of all biosolids were processed with lime stabilization (National lime association, 1999). But at this time, lime addition method was not used in any WWTP in Iran. Methods This study was accomplished in two-bellow section on the biosolids of Ahwaz WWTP, over 12 months from July 2005 to June ) Investigation of stability and reuse potential of disposal biosolids: Samples were tested for stability and reuse potential indexes such as: the ratio of volatile solids to total solids (VS/TS), fecal coliform (FC) number and the number of helminthes ova. Samples were taken at the biosolids outlet from WWTP. Finally, the characteristics of disposal biosolids were compared to the biosolids stabilized indexes, which were recommended by USEPA (USEPA, 1999). 2) Efficiency of lime addition for Ahwaz WWTP disposal biosolids stabilization In this section, a glass reactor with 30-liter capacity and an electrical mixer with variable round per minute were used. The reactor was loaded by raw biosolids of Ahwaz WWTP. Then sufficient amount of hydrate lime (due to dry solids percent of biosolids) was added and mixed to the biosolids. Stability and reuse potential of biosolids in the reactor was checked along 4 weeks. During this time, some indexes such as: ph, fecal coliform (FC) number and the number of helminthes ova were analyzed and compared to USEPA criteria s USEPA (USEPA, 1999). 1130

3 For finding the optimum ratio of hydrate lime, this action was done in 5 times. Finally, the optimum ratio was the amount which could be raised the ph of mixture over 12 for 2 hours and held it over 11 for 4 weeks. Analyses were done according to the methods outlined in APHA (APHA, 1995). except for the number of helminthes ova, which was done, by the methods outlined in USEPA (USEPA, 1999). Results and Discussion The characteristics of disposal biosolids from Ahwaz WWTP were presented in table 2. The results showed that, the average amount of VS/TS ratio, fecal coliform and viable helminthes ova densities were 0.65, MPN per gram of dry solids and 314 ova per 4gram of dry solids, respectively. Table 2: Characteristics of disposal biosolids from Ahwaz WWTP The maximum amounts of these criteria s for stabilized sludge are: VS/TS ratio=0.6, (Bruce, 1984), FC density = 1000 (class A), and or (class B) MPN per gram of dry solids, and helminthes ova density = 1ova per 4gram of dry solids (class A) (USEPA, 1995). There are significant differences between the amounts of these parameters in Ahwaz WWTP disposal biosolids with well-stabilized biosolids criteria s (at least P < 0.01). The ratios of gram hydrate lime, which was added to gram dry biosolids in 5 times of reactor loading were 0.2, 0.22, 0.38, 0.35, and respectively (table 3). Table 3: Results of Ahwaz WWTP biosolids lime stabilization The results of the 5 times helminthes ova analyzes on the disposal biosolids and lime stabilized biosolids were presented in table 3. Based on these data s, there is a significant difference between these amounts with 1 MPN/ 4gr.ds that was related to class A of USEPA criteria (P < 0.01) (USEPA, 1995). The ph variations in lime-stabilized biosolids during 5 times of loading were shown in figure 1. This figure showed that ph were held above 12, in 5 times of reactor loading at least for 5 days, 32 days, >50 days, >50 days, and >50 days, respectively. Figure 1. Variations in lime-stabilized biosolids during 5 times of loading. 1131

4 The variation of FC density in lime stabilized sludge during 5 times of reactor loading and the amounts of FC in classes A and B of USEPA were shown in figure 2. This figure showed that for all steps, after the lime mixing to biosolids amounts of FC were decreased to 0 immediately, and were not increased after 50 days, except for 1 st and 2 nd step. Figure 2. Variation of FC density in lime stabilized sludge during 5 times of reactor loading and in classes A and B of USEPA. 1) Investigation of stability and reuse potential of disposal biosolids At the present time, there is not any certain standard from Iranian environmental protection agency for biosolids reuse or disposal. Therefore, we must choose some reliable criteria s such as USEPA standards. The results of VS/TS ratio on disposal biosolids from Ahwaz WWTP indicated that the sludge was raw. Comparison of the microbial quality of disposal biosolids and USEPA criteria showed that the biosolids was not in class A or B conditions. Therefore, this biosolids should not be disposed to environment or used for any purpose (Wegner, 1992). This result is in agreement with the earlier work of Farzadkia, (2001) on some extended aeration activated sludge WWTP in Tehran, Iran (Farzadkia, 2002). At the time of this study, Ahwaz WWTP biosolids were reused as a fertilizer in farmland, this action cased to environmental pollution and dangerous for public health in this area. For this reason, stabilization of this sludge before reusing or disposal should be noted intensively. 2) Efficiency of lime addition for Ahwaz WWTP disposal biosolids stabilization For lime stabilization of biosolids, 0.2 gram of hydrate lime was added per gram of dry solids, in the first time. The ph dropped under 12 after 5 day and FC was growth from 17 th day and increased to per gram of dry biosolids after 30 days. For keeping the ph over than 12 in more days, this ratio was added to 0.22 in the second time. In this step, ph dropped under 12 after 32 day and FC increased to 6680 per gram of dry biosolids after 49 days. For removing this problem in the tired time, 0.38 gram of hydrate lime was added per gram of dry solids of sludge. In this step, ph did not drop under 12 and FC wasn t growing after 50 days past. For minimization of lime dosage in the forth and fifth steps, 0.35 and gram of hydrate lime was added per gram of dry solids of sludge. In these steps, ph did not drop under 12 and FC wasn t growing after 50 days past, too. As indicated in figure 1 and 2, in the lime addition reactor, ph amounts and FC removal efficiency increases with increasing the lime dosage from 0.2 to 0.38 gram Ca(OH)2 per gram of dry solids of biosolids. However, these figures indicate that there is a little benefit in the operating of reactor over than the ratio of Therefore, this amount can be considered as an optimum ratio of lime addition for Ahwaz WWTP biosolids stabilization. 1132

5 The results of microbial analyzes showed that lime stabilized biosolids were classified on class B of USEPA category in the best condition. Based on the studies conducted by Christie, this stabilized biosolids could be beneficially reused as a landfill cover material, poor soil reconditioned, and co-composting material (Christie, 2001). If fertilizer using of disposal biosolids would be noted the microbial quality of mixture must be improved up to class A of USEPA category (WEF, 1995). For finding the class A condition in lime-stabilized biosolids, National lime association recommends to use of quicklime with exothermic reaction could be noted (National lime association, 1999). CONCLUSION Due to these regards, for lime stabilization of raw biosolids of Ahwaz WWTP we suggested gram hydrate lime (77.9%) adds to gram of dry biosolid. This ratio is a cost-effective and efficient for Ahwaz WWTP in the time of study. For another time or another WWTP the optimum amount of hydrate lime should be evaluated by like of this study. REFERENCES Bruce A.M. (1984). Sewage Sludge Stabilization and Disinfections. Chi Chester: Water Research Center/Ellis Harwood Limited. Christie P., Easson D.L., Picton R.P., Love C.P. (2001). Agronomic Value of Alkaline Stabilized Sewage Biosolids for Spring Barley. Agronomy Journal 93, Farzadkia M. (2002). Investigation of Sludge Stabilization and Reuse in Four Small Treatment Plants of Tehran City. Scientific Journal of Hamadan University of Medical Sciences.9 (2), Lue-Hing C., Zenz D.R., Tata P., et al. (1998). Municipal Sewage Sludge Management a Reference Text on Processing, Utilization and Disposal. Lancaster: Technomic Publishing Company. Metcalf and Eddy. (2003). Wastewater Engineering; Treatment, Disposal, Reuse, 3rd ed. New York: McGraw-Hill. National Lime Association.(1999). Using Lime to Stabilize Biosolids. Fact sheet. Standard Methods for the Examination of Water and Wastewater (1998). 20 th edn, American Public Health Association/American Water Works Association/Water Environment Fedration, Washington DC, USA. U.S.Environmental Protection Agency. (1995). Process Design Manual-Land Application of Sewage Sludge and Domestic Septage. EPA/625/R-95/001. U.S.Environmental Protection Agency.(2000). Biosolids Technology. Fact sheet: Alkaline Stabilization of Biosolids. EPA/832-F U.S.Environmental Protection Agency. (1993). 40 CFR Part 503. Standards for use or disposal of sewage sludge; final rules. Federal Reg 1993; 58(32): U.S.Environmental Protection Agency. (1999). Control of Pathogens and Vector Attraction in Sewage sludge. EPA 625/R Venglovsky J., Placha I., Gerseau, G., et al. (2002). Aerobic and Hydrate Lime Stabilization of Sewage Sludge Comparison. Proceeding of the 10 th International Conference of the RAMIRAN Network. Slovak Republic. WEF. (1995). Wastewater Residuals Stabilization. Manual of Practice no. FD-9, Water Environnant Federation, Alexandria. Wegner G. (1992). The Benefits of Biosolids from a Farmers Perspective. Proceedings, The Future Direction of Municipal Sludge Management. WEF Specialty Conference, pp Portland. 1133