VNU fournal of Natural Sciences and Technology, Vol. 29, No. | (2073) 74-27 Accumulation and transpotation of selected heavy metals in thermophilic anaerobic co-digestion of municipal sewage sludge and organic waste Cao Vfi H*gt, Bti Duy Camt, Trinh L€ Hirngt, Bach Quang Dfrng2 tFaculty of Chemistry, VNU IJniversity of Science, 19 LO Thdnh T6ng Str., Hodn Kiilm Dist., Hanoi, Vietnam tvietno* - Korean Centerfor Environmental Research and Training (VKCET) Vietnam Institute of Meteorologt, HydrolgU and Environment (IMHEN) 03 Ddng Thdi Thdn Str., Hodn KiAm Dist., Hanoi, Vietnam Received 06 March 2013 Revised l4 March 2013; accepted 29 March 2013 Abstract. The aims of this research focus on accumulation and transportation of selected heavy metals in thermophilic anearobic co-digestion municipal sewage sludge and organic waste on the laboratory scale. Organic waste was collected from market and sewage sludge was collected from Kim Nguu River in Hanoi city. Organic waste and sewage sludge were mixed on optimal anaerobic digestion ratio. The influent substrate was put into experimental equipment. During experiment, some parameters such as pH, EC were measured daily, others parameters such as COD, heavy metals concentration were measured after 3 to 5 days. The heavy metals content in influent substrates and effluent substrates were paid more attention in this research. This research discoved that the selected heavy metals content in effluent substrate which were increased with order Cd>Pb>Ni>Cr>Cu>Zn. The heavy metal content is lower in influent subtrate and higher in effluent substrate. The heavy metals were easily bleached in to eluted solution in 18 fust days of themophilic anaerobic co-digestion process with order Ni>Cd>Cu>Cr>Zn. The results of research provided data to help readers understand clearly about characteristics of municipal sewage sludge in Hanoi. Base on results of this research to develop sewage sludge troatment methods. Product after treatment could be used as fertilize for soil amendment. Keywords: thermophilic anaerobic digestion, mwricipal sewage sludge, organic waste, heavy metals 1. Introduction Heavy metals which are metals have private density rather than 5glcm'. From wastewater treatment processes, heavy metals were accumulated in sewage sludge. The content and t-or rponaingauthor.Tel:84-904442426. E-mail : hungcv@invitek.com. vn characteristics of sewage sludge depend on properties of wastewater sources [2]. Urban area in Vietnam where still exist a lot small workshops in the city. Therefore, the properties of municipal wastewater are complicated which lead to complicated composition of municipal sewage sludge. Specialy, the heavy metals contents is very high in sewage sludge. t4 C.V. Htng et al. I WU lournal of Nntural Sciences and Technology, Vol. 29, No. 1 (20L3) L4-21 t5 Now a day,. treating municipal sewage sludge is necessary in Vietnamese urban area. However, finding the suitable treatment method to orient reduces, reuses and recycles are difficult. In order to meet this requirement need to implement more investigation on municipal sewage sludge. For example, in Japan where have high technology in development of municipal treatment method. After treatment, the municipal sewage sludge was used arcund 30Yo of mass as fertilize. This ratio will be raised in the future [5]. In this research, focus on accumulation and transportation of selected heavy metals in thermophilic anearobic co-digestion of municipal sewage sludge and organic waste. Results ofresearch are provided data to develop treatment method with airn to use product as fertilizer for soil amendment [4]. 2. Material and methods 2.1. Pilot equipment The pilot equipment consists of single cylindrical reactor (diameter 0.6m, height 0.8m) made from stainless steel with available volume is 40 liters (fig. l). The out site is heat keeping layer. The reactor also is equipped with a thermal insulation and the temperature is kept constant at 55'C (thermophilic condition). Gas volumetric flow measurement is used to measure gas volume after 24 hour. The effluent substrate was sampled daily though valve in the bottom of reactor and pH, EC were measured. Others parameters such as COD, heavy metals were measured after 3 days to 5 days follow experiment plan in order to assess the stabilization process. Fig.l. Photo of the pilot equipment. 2. 2. Substrates characteris tics The anaerobic co-dieestion involved two different substrates: - The municipal sewage sludge was sampled from Kim Nguu River near from Lac Trung Bridge. - The organio waste comes from market. Municipal sewage sludge was removed inert substances such as bridges, stones, special solid waste after collection. The sewage sludge has to be smooth to avoid obstructed in reactor. The organic fraction has quite variable characteristics however its average composition can be roughly estimated as 30%o animal origin and 70o/o vegetable origin. It was grinded by grinding machine and mixed with municipal sewage sludge follow ratio three part of organic waste by volume and one part of municipal sewage sludge by volume before put into reactor. Table l. Input subshates composition r ' ,' r Vuss Vo* v inFsrbsrde \L/ (%) (%\ DMSS(s/rrrl) (?il) 25 75 t.441 1.247 VMSS: Volume of municipal sewage sludge; VOW: Volume of organic waste; DMSS: density of municipal sewage sludge; DOW: density of organic waste. 30 t6 C.V. H*ng et aI. / WIJ Journal of Natural Sciences and Technology, Vol. 29, No. 1 (201'3) 14-21 2.3. Methods The experiment was implemented in batch type with optimal ratio of municipal sewage sludge and organic waste is l/3 for anaerobic digestion t6]. The component of influent substrate was shown in table 1. EC and pH value were determined bY Eutech Con 700 and Cyberscan pH 110. COD total was determined by titraction with KzCrzOz method. Heavy metals were determined by ICP OES method. Preparing solid samples for heavy metals determination After sampling, samples were dryed at 60oC during 24 hours. After that, the samples were grinded and kept in anti-moisture vase. Each of samples was scaled one gram and put into Teflon tubes. Continuoustly put 9 ml HNO3 acid 620/o and I ml HzOz 30oh. T\e heating mechanism of microway oven was divided two steps: Step 1: the temperature need to reach 165"C around 2 minutes, the max pressure could be 350 psi, retention time is 4 minutes. Step 2: The temperature need to reach 175oC around 3 minutes, the max pressure could be 350 psi retention time is 20 minutes. The samples were cooled automatically to ambient temperature. After that they were determined by ICP OES. Preparing eluted solution for heavy metals determination Scale exactly 10g dry substrate and put into bottle 250 ml, add 100 ml distilled water and shake around 24 hours. After that, use spin filter to collect eluted solution and filled by filter paper before determination of heavy metals content by ICP OES method. 3. Results and discussions 3.1. Variations of pH and EC value Eo A 7,4 7,6 7,a 7 6,4 6 ,+PHi Time (day6) Fig.2. Variation of pH value. The variation of pH'value was shown infig.2. This variation is characteristic of anaerobic digestion. In the first phase, pH value has decreasing trend. It is suitable to organic compound digestion [3]. The lowest pH value in this experiment is 6.78 after 9 days. During digestion, pH value continoustly increases and stable at the stability phase ofdigestion process. 5 9 t3 17 21 25 A 837 41 15 49 S 5761 S69 n 77 01 S ^ 1300 t rroo !, 39oo 3700 3500 3300 31 00 2900 2700 2500 Tlm (days) Fig. 3. Variation of EC value . C.V. Httng et aI. l:'.l lJ lournal of Natural Sciences andTechnology, Vol.29, No. 1 (2013) 14-21 17 The variation of EC value is suitable rule of anaerobic digestion. Firstly, EC value usually increases. After that, it decreases and stable. 3.2. Variation of COD| e 100000 P [ ,*oo a 80000 70000 60000 5oom 40000 0 5 t0 t5 20 25 30 35 40 45 50 55 60 65 70 75 60 65 90 F_:SqQ,fqLr*ri l rime(daF) Fig.4. Variation of CODI value. Figure 4 shown variation of CODI depend on time. This variation is suitable to anaerobic digestion. In the first stage CODt increase in 5 to l0 days and decrease during anaerobic digestion take place. The variations of pH, EC, CODI during digestion process affirm that the process take place in this experiment that is anaerobic digestion. 3.3. The accumulation and transportation of selecled heavy metals Accumulation of heat'y metals in municipal sewage sludge Municipal wastewater in Hanoi city not only contains household wastewater but also contains wastewater from small workshops. Therefore, the properties of municipal wastewater are very complicated, Similar to popular wastewater treatment process, municipal wastewater though out sewage system that take place process such as physical processes, chemical processes and biological processes [1]. The accumulation of heavy metal in sewage sludge depends on characteristic of wastewater treatment plant system and its operation [2]. Therefore, the accumulation of heavy metals in municipal sewage sludge is different on each of zones as well as each of country. The transportation of heavy metals Transpoftation, biological characteristics or toxic behaviours of heavy metals mainly depend on chemical properties of each heavy metal as well as compound forms of heavy metal in sewage sludge [1]. It is difficult to determine a suitable method for treatment municipal sertage sludge with orient using product to soil amendment. Therefore, it is necessary to pay more attention to compound form of heavy metals in sewage sludge as well as its transportation during treatment process [l]. Efficiency of removing heavy metals from sewage sludge depends on compound form of heavy metals. Usually, heavy metals exist on a lot of compounds such as sunfide, hydroxide, silicate, coordinate form with organic legends. There are a lot of mechanisms effect on transform of heavy metal compound in sewage sludge which are effect on transporting and bleaching of heavy metal from sewage sludge. In which, it is necessary to pay more attention to heavy metal mobilization mechanisms in sewage sludge treatment by anaerobic digestion. The microorganism activities oxidized sunfide compounds which promote bleaching of heavy metals into aqueous phase. Transpoftation mechanism follows equation: Thio-oxidans MeS + 2O.t: MeSOa l8 C.V. Hung et al. / WU lournal of Natural Sciences and Technology, Vol. 29, No. 1 (2013) 14-2'1 Though this mechanism, heavy metals exist on sunfide form in sewage sludge such as NiS, CuS, ZnS could be bleached [1]. However, the microorganism activities are affected by conditions of treatment process such as temperature, pH, and initial substrate component. Treatment process is implemented in thermophilic that have heavy metals bleaching rather than mesophilic condition. The pH value not only effect on healy metals bleaching follow chemical mechanism but also indirectly effect on microorganism developing that cause to effect on transformation of healry metals in substrate. Thus. affirm that the accumulation and transportation of heavy metal in treatment process depends on initial substrate and technology conditions. o 5 1j 17 27 $ 43 55 6t 71 79 67 rh. {d.y.l F-l;l:::l!': Fig. 7, Variations of Cu content in dry substrates and eluted solutions. t fg is a s. ru; ,* EE E 'sE l@o s a m 1s 1@ M 7m: m 3a ru ie 4mI w! ro lm 0 t ?r{ ;E 14 :E 1@ t tm 4 m o l1m T f, 140 gs',0 i9 tm f;m L60 40 x 0 _i : ll i7 zr % 43 55 61 71 7e 07 rrh' (d!v') I - N in dy .u*tal +Ni In duld !ddr6 ie >i :E g E 0 5 11 '17 27 36 43 55 61 71 79 87 nm(dayr) i J-,"0o*,a* '"i""o""'*f Fig. 5. Variations of Cadmium content in dry substrates and eluted solutions. 2m 150 1m 50 0 0 5 11 17 27 38 43 $ 61 71 79 87 Tlme (fiy.| Fig. 6. Variations of Chromium content in dry substrates and eluted solutions. Fig. 8. Variations of Nickel content in dry substrates and eluted solutions. & & 40 & 0 05111727$435561 sr Tlh. {d.yt) -Pb h dry subskal +Pb n 6lul* sdulrd Fig. 9. Variations of Lead content in dry substrates and eluted solutions. I lld 1i ii !9 E l-br4Dnrd- Fig. 10. Variations of Zinc content in dry substrates and eluted solutions. 60g ; iE d 2Qt 10 0 & m T !; I o 6 ru I= re ! 8 riirc 1200 1m m ffi m 2@ 0 '*i @t ! m 3t I 4Mi *I E 600 g soo E roo i soo : 200 t 100 0 CdOOTNFbZn E H€W metals content in lnitial samples I Ilil il C.V. turng et al. / WIJ lournal of Natural Sciences and Technology, VoI. 29, No. L (201.3) 1.4-27 l9 The increasing percentages of heary metals content follow the order Cd>Pb>Ni>Cr>Cu> Zn. b H.""y *trla EA€qe reent4€s hry metals deased In ficl 18 days rAEq€ re€nt4es baw melds desd der 10 drys Fig. I L Heavy metals content in initial substrate. Fig.13. Average heavy metals released. Fig. 13 descriped the average releasing of heavy metals in first 18 days is higher than after 18 days of treatment process. This phenomenon is quirely appreciate to decreasing of pH value in l8 first days of treatment process. In the first stage, the organic digestion creates organic acids and ammonium that have high coordinate abilities with heary metals. pH value increases in after stage of treatment process but the releasing ability transporting into aquatic phase of heavy metals was lower than first stage. Therefore, this research shown that all selected healy metals easily transporting into aquatic phase during 18 first days of treatment process. ln which, the transporting ability follows order Ni>Cd>Cu>Cr>Zn. 4. Conclusions Though researching results, we could conclude like that: The accumulation and transportation of selected heavy metals in thermophilic anearobic co-digestion of municipal sewage sludge and organic waste depends on a lot of factors such as initial substrate characteristics, technology coirditions, implement method. . . ^ 100 :l ^^ g-^ J^n 5"' Eso i," I.^ o 820 Ito 0 :( E ! I 80 Fig. 12. Heavy metals increasing in effluent substrate. This research shown that anaerobic digestion is the cause to increase heavy metals content in effluent substrate. During anaerobic digestion, the biodegradation of organic compounds with the end products such as CHa, CO2, NH3 also heavy metals are not biodegradable and negligible evapour. This is the main cause to make increase heavy metals content in dry effluent subtrate [2]. Fig.12 shown that the lower heavy metal content in initial substrate the higher heavy metal content in effluent substrate after treatment process. 20 C.V. Htng et aL / WU lournal of Natural Sciences and Technology, Vol. 29, No. 1 (2013) 14-21 Experiments shown that heavy metals content of effluent substTate increase after treatment process follow order Cd>Pb>Ni>Cr> Cu>Zn. Heavy metal content is lower in initial substrate, it is higher in effluent substrate after treatment process. This research shown that all selected heavy metals easily transport into aquatic phase during 18 first days of treatment process. In which, the transport ability follows order Ni>Cd>Cu>Cr>Zn. This research contributed data about characteristics of municipal sewage sludge. Base on collected data to build suitable releasing heary metals method in treatment process. The product of treatment process could be used for soil amendment. References tll Ashish Pathak, M.G. Dastidar, T.R. Sreckrishnan, Bioleaching of heavy metals from sewage sludge: A review, Joumal of Environmental Managemenr 90 (2009) 2343- 2353. Kangala B. Chipasa, Accumulation and fate of selected heavy metals in a biological wastewater treatment system, Waste Management 23 (2003) 135-143. B. Bilitewski, Georg Haerdtle, Klaus Marek, Waste Management, Springer, 1 994. Brian J. Alloway, Andrew P. Jackson, The behaviour of heavy metal in sewage sludge- amended soils, The Science of the Total Environment, | 00 (1991) 1 5l-176 l5l, Ayumiito, Teruyuki Umita, Jico Aizawa, Toshiyuki Takachi, Koji Morinaga, Removal of heavy metals from anaerobiccally digested sewage sludge by a new chemical method using ferric sulfat, Wat. Res. Vol.34, No.3, pp.75 l- 758. 2000. Cao Vu Hung, Bui Duy Cam, Thermophilic anaerobic co-digestion of source selected organic waste and municipal sewage sludge: Case study in Hanoi, International Conference on Sustainable concepts for Industrial wastewater treatment and Industrial zones management (SCIWT 2012, October l0 - ll, 2012. Hanoi. Vietnam. l2l t3l t4l L"l t6l Sg tich tu vd vfln chuy6n cua mQt sO kim loai nAng trong qu6 trinh 6n dinh birn thai t6t ngp r6c hiru co bdng phucrng ph6p l€n men nong Cao Vfl H*gt, Biri Duy Camr, Trfnh L0 Htngr, Bach euang Dfrng2 tKhoa hda hoc, Trudng Dai hoc Khoa hoc n{ nhiAn, DHQGHN, t9 LO Thdnh T6ng, Hodn Kitim, Hd NQi, ViQt Nam tTrung tdm Nghiin c*u Ddo tqo Vi€t Nam - Hdn QuiSc IKCET) Vi€n Khoa hoc Khi trong Thuy vdn vd M6i trudng (IMHEN) Trong nghi€n criu ndy tflp trung nghi€n cr?u sg tich t.u vd v4n chuytin cria mQt s6 kim logi n{ng trong qu6 trinh 6n tllnh btn thai k.it hqp v6i r5c hfru co bing phuong ph6p l€n men n6ng tr6n qui md phong thi nghi€m. R6c thAi hiru co clugc lga chon vd bin thAi tluqc l6y tir hQ thdng s6ng tho6t nudc thdnh ph6 trdn tlia bdn thdnh ptrO Ha NOi. R6c hiru co vd bun thAi duoc pnO; tr6n voi ry lQ thich hop C.V. Htmg et aI. /WU lournal of Natural Sciences andTechnology,Vol.'29, No. 1 (2073) L4-21 2l theo hu6ng ttii uu qu6 trinh phAn hriy y6m khi. H6n hqp bin thii vdrbc hftu co dugc dua vdo m6 hinh thi nghipm hogt ddng theo kii5u m6. Trong su6t qu6 trinh ti6n hdnh thi nghi€m c6c chi ti€u nhu pH, dq ddn diQn (EC), th€ tfch khi biogas (Vbiogas) clugc do hdng ngdy, c6c chi sti kh6c nhu COD t6ng, kim lo4i ning dugc do djnh k! theo k6 ho4ch th\rc nghiQm. Hdm lugng kim loai trong dAu vdo vd sin phAm dAu ra cria qu6 trinh xri lf duoc <tic biet quan tAm trong nghi€n cr?u. Nghi6n cr?u dd chi ra dugc c6c kim loai ndng c6 hdm lugng ting l€n trong sdn phAm sau qu6 trinh 6n ttinh v6i thf tg sau: Cd>Pb>Ni>Cr>Cu>Zn, kim loai cdng c6 hdm luqng th6p trong nguy6n liQu dAu vdo, c6 phAn trim tlng cirng cao trong sin phAm sau 6n tlinh. Nghidn cfu cfing tld chi ra ciic kim 1o4i n[ng d6 ddng v{n chuy6n vdo pha nu6c hon trong giai tlo4n 18 ngdy dAu cria qu6 trinh 6n dinh v6i thf t.u linh cfQng cria c6c kim lo4i nhu sau: Ni>Cd>Cu>Cr>Zn. Ktit qu6 cria nghiOn criu g6p phAn hi6u s6u hcrn .rrd birn thii tho6t nudc tlii5n hinh tai Hd NOi tr€n co sd d6 <t€ xu6t phuotrg 5n thich hqp cho viQc lo4i bd kim topi n{ng ldm tiAn dO sri dpng sdn phAm sau xft ly cho viQc cai tao d6t ndng nghi6p. . research, focus on accumulation and transportation of selected heavy metals in thermophilic anearobic co-digestion of municipal sewage sludge and organic waste. Results ofresearch are provided. The aims of this research focus on accumulation and transportation of selected heavy metals in thermophilic anearobic co-digestion municipal sewage sludge and organic waste on. of Natural Sciences and Technology, Vol. 29, No. | (2073) 74-27 Accumulation and transpotation of selected heavy metals in thermophilic anaerobic co-digestion of municipal sewage