Electrochemical oxidation of the effluent from anaerobic digestion of dairy manure

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    The electrochemical oxidation of the digested euent from anaerobic digestion of dairy manure was investigated in this study.The digested euent sample containing with suspended solids was pretreated by ltration for the electrochemical experiment. The

    serious problem for livestock production. Anaerobic

    process for removing nitrogen and residue organic sub-

    in recent years. Both organic pollutants and NH4-N in

    2.1. Anaerobic digestion

    The digested euent used in this study was collectedfrom a full-scale anaerobic digester of ObihiroUniversity of agriculture and veterinary medicine


    * Corresponding author. Tel.: +81 155 49 5515; fax: +81 155 495519.

    E-mail address: umetsu@obihiro.ac.jp (K. Umetsu).

    Bioresource Technology 97 (20960-8524/$ - see front matter 2005 Elsevier Ltd. All rights reserveddigestion has become an option for sustainable treat-ment of livestock manure, converting it to biogas andeuent. Digested euent from anaerobic digestion oflivestock manure usually contains high strength ofammonium nitrogen (NH4-N) and persistent organicsubstances. The components in digested euent hadbeen applied as fertilizer for recycling of nutrients backto agricultural eld (Salminen et al., 2001; Umetsu et al.,2002). The excessive spreading of livestock manure onthe eld should be attributable to nitrogen pollution infarming areas (Woli et al., 2004). A simple and eective

    wastewater containing chloride can be destroyed electro-chemically (Chiang et al., 1995). In this work the euentfrom anaerobic digestion of dairy manure was treatedby the application of electrochemical oxidation. Thepurpose of this study was to identify the main para-meters inuencing the performance of an electrochemi-cal oxidation process.

    2. Methodsinuence of direct anodic oxidation and indirect oxidation was evaluated through the use of dimensionally stable anode (DSA) andTi/PbO2 as anode. The decreasing rate of chemical oxygen demand (COD) was higher at lead dioxide coated titanium (Ti/PbO2)electrode than at DSA, however the DSA was preferred anode for the decrease of ammonium nitrogen (NH4-N) due to the controlof ammonium nitrate (NO3-N) accumulation. The results showed that the ltration of suspended solids as a pretreatment and addi-tion of NaCl could improve the whole removing eciency of NH4-N in the digested euent on electrochemical oxidation. 2005 Elsevier Ltd. All rights reserved.

    Keywords: Ammonium nitrogen; COD; DSA; Euent from anaerobic digestion; Electrochemical oxidation

    1. Introduction

    Waste management has been widely recognized as a

    stances is required as a posttreatment of the euentfrom anaerobic digestion. The electrochemical oxidationtreatment of various wastewaters has been investigatedElectrochemical oxidaanaerobic digestio

    Ikko Ihara a, Kazutaka Umetsu a,*, Ka Department of Agro-Environmental Science, Obihiro University of A

    b Graduate School of Engineering, Tokyo Metropolitan

    Received 16 February 2005; received in reAvailable onli

    Abstractdoi:10.1016/j.biortech.2005.07.007shi Kanamura b, Tsuneo Watanabe b

    lture and Veterinary Medicine, Inada-cho, Obihiro 080-8555, Japan

    versity, 1-1 Minami-Osawa, Hachioji 192-0397, Japan

    form 7 July 2005; accepted 11 July 2005August 2005n of the euent from

    006) 13601364

  • treatment.

    3. Results and discussion

    3.1. Variation of parameters during electrochemical

    oxidation at DSA

    The diluted sample with 0.5 g of NaCl, pretreated by0.5 lm membrane lter was tested for the electrochemi-cal oxidation using a DSA (Fig. 1). The concentration ofCOD was reduced by 32% in 9 h. In a previous work,the electrochemical oxidation applying for wastewatertreatment was explained by a direct anodic oxidationor an indirect oxidation (Chiang et al., 1995). In thedirect anodic oxidation, the organic pollutants weredestroyed on oxide anode by electrochemical conversionor combustion (Comninellis, 1994). In the indirectoxidation, the electrogenerated oxidant such as hypo-chlorite (Comninellis and Nerini, 1995) or peroxodisul-phates (Canizares et al., 2003) destroyed the pollutantsin the bulk solution. The concentration of acetatewas increased consistently whereas the COD wasdecreased from the beginning. The result showed thatthe electrochemical oxidation at DSA for the wastewatercontained chloride had low degradability to acetic acid.The NH4-N was decreased rapidly with time. Thedecrease of NH4-N could be explained by indirect oxida-tion with hypochlorite.

    I. Ihara et al. / Bioresource Technology 97 (2006) 13601364 13612.4. Analytical method

    Chemical oxygen demand (COD) was determined bydichromate method. Ammonium nitrogen (NH4-N)was determined using salicylate reaction. The concen-trations of these analytical parameters were measuredby a HACH DR4000 spectrophotometer. Ammoniumnitrate (NO3-N), chloride ion, hypochloride ion andacetic acid were analyzed by capillary electrophoresis(CE) system (Agilent Technologies, G1600A). Thebasic anion buer and a fused silica capillary with104 cm in length and 50 lm internal diameter wereobtained from Agilent technologies. The temperaturecontrolled cartridge for fused silica capillary was setat 30 C and the applied dc voltage was 30 kV. Thewavelength of diode array detector was set at 350 nm(signals)/275 nm (reference). Before the CE analysis,the euent sample was pretreated by 0.45 lm pore size2.3. Experiments of electrochemical oxidation

    The electrochemical oxidation experiment was con-ducted in a glass beaker, equipped with a 100 50 mmmesh anode and a plate cathode. The anodes were adimensionally stable anode (DSA) based on mixed oxi-des of RuO2 + IrO2 and lead dioxide coated titanium(Ti/PbO2) electrode. The stainless steel was used as cath-ode. They were placed vertically and parallel to eachother with an electrode gap of 10 mm in a beaker. Theelectrochemical oxidation was carried out at a constantcurrent of 1.5 A using a DC power supply. The samplesolution was agitated by a magnetic stirrer. The surfacebubbles were recycled by a peristaltic pump forantifoam.(Hokkaido, Japan). A 60 m3 anaerobic digester was in-stalled next to free stall barn and was operated withdairy manure slurry at a digester temperature of 55 C.In the coldest season, average biogas production was150 m3/day, consisting of 56% methane gas with an aver-age loading rate of 6.75 kg/m3/day which established ahydraulic retention time of 13 days at an average ambi-ent temperature of 15 C and slurry temperature of2 C.

    2.2. Pretreatment for digested euent

    To remove suspended solids, the euent sample waspretreated with membrane lters. After the ltrationwith a nylon membrane lter (pore size: 37 lm), thesample was ltered with a hollow ber membrane (poresize: 5.0 or 0.5 lm). All ltrated samples were diluted 1:2with distilled water before electrochemical oxidationmembrane lter.0





    0 2 4 6 8 100





















    time (h)






    H (m


    E (V



    NH4 -N NO3 -N ClO -

    Cl -

    pH (-

    ) CO

    D (m

    g / L


    H 4-N

    , NO 3


    , Cl



    ) Fig. 1. Electrochemical oxidation at DSA with addition of 0.5 g NaCl.

  • Hypochlorite is generated as the product of hydro-lysis of chloride. The decreasing process of NH4-Nmight be regarded as similar to the chemistry of the Sel-leck-Saunier breakpoint phenomenon (Chiang et al.,1995; White, 1998). The electrochemically generatedhypochlorite was consumed to produce nitrogen fromammonium ion. Since the sample contained 1496 mg/Lof chloride ion at the start of the experiment and DSAhad high catalytic properties for chlorine evolution(Trasatti, 2000), hypochlorite was eectively producedand responsible for NH4-N decrease during the electro-chemical oxidation. The data showed that NH4-N wasvanished in 8 h, and then hypochlorite ion was detected.

    3.2. Inuence of NaCl addition

    Fig. 2 showed the inuence of the chloride ions onelectrochemical oxidation using DSA. The diluted sam-

    not predominant in the degradation of organics in thedigested euent.

    3.3. Comparison of anode materials between

    DSA and Ti/PbO2

    The inuence of anode material on electrochemicaloxidation was examined with DSA and Ti/PbO2 anodefor the decrease of NH4-N and COD (Fig. 3). Thedecreasing rate of NH4-N was higher at DSA than atTi/PbO2. It was indicated that the DSA had higher cata-lytic property for chlorine evolution. In contrast, theaccumulation rate of NO3-N was higher at Ti/PbO2than at DSA. The data showed that NO3-N was theintermediate product in the electrochemical oxidationof NH4-N. It was signicant that the electrochemicaloxidation with DSA can prevent the accumulation ofNO3-N. White (1998) noted the side reaction fromammonium ion to nitrogen gas in the breakpoint chlori-nation, which was aected by factors such as the initialratio of chloride to NH4-N, pH and alkalinity.

    Fig. 3 also illustrated the degradation of COD incomparison with DSA and Ti/PbO2. It was clear that

    00 2 4 6 8 10

    time (h) Fig. 3. Eect of anode material for the decrease of NH4-N and CODduring electrochemical oxidation with addition of 0.5 g NaCl.

    1362 I. Ihara et al. / Bioresource Technology 97 (2006) 13601364ple used in the experiments contained approximately700 mg/L of chloride ion. When 0.5 or 2.0 g of NaClwas added, the decreasing rate of NH4-N was increaseddramatically. The increased concentration of chlorideion had positive inuence for the enhancement in therate of NH4-N decrease. An increase in the concentra-tion of chloride ion produced a high generation rate ofhypochlorite. The result also indicated that the dilutedsample of digested euent had only a low concentrationof chloride ion for the decrease of NH4-N on electro-chemical oxidation. To achieve an economical opera-tion, the addition of adequate amount of chloride ionwas required for the digested euent.

    In contrast, the addition of NaCl had less eective forthe decrease of COD during electrochemical oxidation.The generated amount of hypochlorite increases withhigh initial concentration of chloride ion on constantcurrent electrolysis. The result indicated that the indirectoxidation caused by electrogenerated hypochlorite was







    0 2 4 6 8

    no addition

    0.5 g NaCl added

    2.0 g NaCl added

    time (h)


    4 -N


    Fig. 2. Eect of NaCl addition for the decrease of NH4-N during

    electrochemical oxidation at DSA.2000









    COD (DSA)COD (Ti/PbO2)

    NH4-N (DSA)NH4-N (T i/PbO2)NO3-N (DSA)NO3-N (T i/PbO2)


    c. (m

    g / L

    ) co


    (mg /

    L) the decreasing rate of COD was higher at Ti/PbO2

  • anode than at DSA. The indirect oxidation with electro-generated hypochlorite might have little inuence of thededuction rate of COD. Thus, it was considered thatthe direct anodic oxidation was allowed to enhance thedecreasing rate of organic pollutants contained in thedigested euent. The dierential decrease of CODbetween DSA and Ti/PbO2 could be explained by dier-ent two states for active oxygen at anode surface ondirect anodic oxidation (Comninellis, 1994). The physi-cally adsorbed active oxygen (OH) can cause thecombustion of organic compounds at the surfaceof the inactive electrode such as Ti/SnO2 and Ti/PbO2(Simond et al., 1997). In contrast, the chemicallyadsorbed active oxygen can favor selective oxidationof organic compounds with active electrode such as Pt,Ti/IrO2 (Comninellis, 1994) and DSA (Polcaro et al.,2000). The result showed that the anode material wasessential parameter for the elimination of both organicpollutants and NH -N for wastewater treatment by

    tion of Science (JSPS) for the future program.

    Electrochemical oxidation of several chlorophenols on diamondelectrodes. Part I: Reaction mechanism. J. Appl. Electrochem. 33,

    house wastes as fertilizer in agriculture. Biores. Tech. 78, 8188.

    I. Ihara et al. / Bioresource Technology 97 (2006) 13601364 13634

    electrochemical oxidation.

    3.4. Eect of pretreatment by membrane ltration

    To achieve more eective degradation, ltration bymembranes was performed as a pretreatment to evaluatethe ecacy for the electrochemical oxidation treatment.Fig. 4 illustrated the eect on dierent pore sizes of amembrane lter for the pretreatment of electrochemicaloxidation. The decreasing rate of NH4-N for the pre-treated sample with 0.5 lm membrane lter was higherthan with 5.0 lm. The enhancement of decreasing rateof NH4-N can be explained by taking into account thatsuspended solids was separated by membrane lter. Itwas noted that suspended solids contained in waste-water would impede the electrochemical oxidation(Kim et al., 2003). In general, the euent from anaero-








    5.0 m0.5 m

    time (h) 80 2 4




    Fig. 4. Eect of pretreatment with membrane ltration for thedecrease of NH4-N during electrochemical oxidation at DSA (NaCl

    0.5 g added).Simond, O., Schaller, V., Comninellis, C., 1997. Theoretical model forthe anodic oxidation of organics on metal oxide electrodes.Electrochim. Acta 42, 20092012.

    Trasatti, S., 2000. Electrocatalysis: understanding the success ofDSA. Electrochim. Acta 45, 23772385.

    Umetsu, K., Kondo, R., Tani, M., Hayashi, T., 2002. Fertilizer valueof anaerobically co-digested dairy manure and food processing917927.Chiang, L.C., Chang, J.E., Wen, T.C., 1995. Indirect oxidation eect

    in electrochemical oxidation treatment of landll leachate. WaterRes. 29, 671678.

    Comninellis, C., 1994. Electrocatalysis in the electrochemical conver-sion/combustion of organic pollutants for waste water treatment.Electrochim. Acta 39, 18571862.

    Comninellis, C., Nerini, A., 1995. Anodic oxidation of phenol in thepresence of NaCl for wastewater treatment. J. Appl. Electrochem.25, 2328.

    Kim, T.H., Park, C., Shin, E.B., Kirm, S., 2003. Eects of Cl-basedchemical coagulants on electrochemical oxidation of textile waste-water. Desalination 155, 5965.

    Polcaro, A.M., Palmas, S., Renoldi, F., Mascia, M., 2000. Three-dimensional electrodes for electrochemical combustion of organicpollutants. Electrochim. Acta 46, 384389.

    Salminen, E., Rintala, J., Harkonen, J., Kuitunen, M., Hogmander,H., Oikari, A., 2001. Anaerobically digested poultry slaughter-References

    Canizares, P., Garca-Gomez, J., Saez, C., Rodrigo, M.A., 2003.bic digestion of livestock manure contained high con-centration of suspended solids. The result indicatedthat the pretreatment such as membrane ltration wasimportant for the economical operation on electrochem-ical oxidation of high concentration of wastewater.

    4. Conclusions

    The electrochemical oxidation could be feasible forthe treatment of the euent from anaerobic digestionof dairy manure. Both NH4-N and COD were decreasedin proportion to the electric charge. The high chlorideconcentration was possible to accelerate the indirect oxi-dation for the decrease of NH4-N. The electrochemicaloxidation combined with pretreatment of membrane l-tration allowed also more eective decrease of NH4-N.DSA showed the advantage of decreasing NH4-N buthad lower eciency of organic pollutants. The resultsconcluded that the DSA was more suitable anode thanTi/PbO2 to achieve the control of nitrate accumulation.


    This work was supported by Japan Society Promo-wastes. In: Takahashi, J., Young, B.A. (Eds.), Greenhouse Gases

  • and Animal Agriculture. Elsevier Science B.V., Amsterdam,Netherlands, pp. 331342.

    White, G.C., 1998. Handbook of chlorination and alternative disinfec-tants, fourth ed. John Wiley & Sons Inc., New York, pp. 227243.

    Woli, K.R., Nagumo, T., Kuramochi, K., Hatano, R., 2004. Evalu-ating river water quality through land use analysis and N budgetapproaches in livestock farming areas. Sci. Total Environ. 329,6174.

    1364 I. Ihara et al. / Bioresource Technology 97 (2006) 13601364

    Electrochemical oxidation of the effluent from anaerobic digestion of dairy manureIntroductionMethodsAnaerobic digestionPretreatment for digested effluentExperiments of electrochemical oxidationAnalytical method

    Results and discussionVariation of parameters during electrochemical oxidation at DSAInfluence of NaCl additionComparison of anode materials betweenDSA and Ti/PbO2Effect of pretreatment by membrane filtration



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