removal and recovery of nutrients as struvite from anaerobic digestion residues of poultry manure
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Removal and recovery of nutrients as struvite fromanaerobic digestion residues of poultry manureY.D. Yilmazel a & G.N. Demirer aa Department of Environmental Engineering, Middle East Technical University, 06531 Ankara,TurkeyPublished online: 13 Jun 2011.
To cite this article: Y.D. Yilmazel & G.N. Demirer (2011) Removal and recovery of nutrients as struvite from anaerobicdigestion residues of poultry manure, Environmental Technology, 32:7, 783-794, DOI: 10.1080/09593330.2010.512925
To link to this article: http://dx.doi.org/10.1080/09593330.2010.512925
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Vol. 32, No. 7, May 2011, 783794
ISSN 0959-3330 print/ISSN 1479-487X online 2011 Taylor & FrancisDOI: 10.1080/09593330.2010.512925http://www.informaworld.com
Removal and recovery of nutrients as struvite from anaerobic digestion residues of poultry manure
Y.D. Yilmazel and G.N. Demirer*
Department of Environmental Engineering, Middle East Technical University, 06531 Ankara, Turkey
Taylor and Francis
Received 11 January 2010; Accepted 30 July 2010
The removal and the recovery of nutrients, namely nitrogen (N) and phosphorus (P) from anaerobically digested andsolidliquid separated manure effluents via struvite precipitation were investigated. Both the liquid and the solidphases of the poultry manure digester effluent were subjected to struvite precipitation experiments. The Mg:N:Pmolar ratio of 1:1:1 in the liquid phase resulted in an average NH
-N removal efficiency of 86.4%, which increasedto 97.4% by adjusting the Mg:N:P ratio to 1.5:1:1. The acidic phosphorus-dissolution process was applied to the solidphase of the effluent to obtain a phosphorus-enriched solution. Nutrient recovery experiments with NaOH as thebuffering reagent were conducted with and without addition of external chemicals (Mg and P sources) to evaluate theinfluence of the Mg:N:P molar ratio, the Mg:P molar ratio and pH. All the experiments depicted complete PO
-P(99.6100.0%) and partial NH
-N (3.365.6%) recoveries from the phosphorus-enriched solution.
anaerobic digestion; poultry manure; nutrient recovery; phosphorus dissolution; struvite
The poultry and the livestock industries are growingrapidly and this has led to large quantities of animalwaste production. Atuanya and Aigbirior  reportedthat the poultry production is the fastest growingcottage industry, and estimated the annual solid wastegeneration from poultry farms at the level of millionsof tons. Gungor-Demirci and Demirer  reported thatthe production of cattle and poultry manure in Turkeywas approximately 20 million tons of dry matter in2000. Direct land application of manure is the mostpreferred method of utilization, but it is not alwaysfeasible. Because nutrients in manure are not necessar-ily present in the same proportion needed by the crops,if applied at a rate higher than plant uptake, there is agreat risk of nutrient leaching and run-off resulting ineutrophication of surface waters . Moreover, thehigh prevalence of pathogenic microorganisms in freshpoultry poses a potential threat to human healththrough contamination of water bodies from untreatedpoultry wastewater . If the land to be used for directapplication is distant or the location is sensitive toodour, some type of manure treatment may be required.Some of the currently used options for the managementof poultry manure such as landfilling and incinerationlead to the loss of nutrients as well as environmentalproblems .
Anaerobic digestion (AD) is an established technol-ogy to convert animal waste into profitable by-productsas well as to reduce the relevant air, water and soilpollution problems [1,2,6,7]. However, because ADremoves mainly carbon, additional processes to removenitrogen (N) and phosphorus (P) should also be used tomeet the stringent effluent criteria. Moreover, there is ashift from the removal to the recovery of nutrients as aresult of increasing concerns regarding limited naturalresources and the importance given to the sustainabletreatment technologies.
Crystallization of N and P in the form of magnesiumammonium phosphate hexahydrate (MgNH
O,struvite or MAP) is one of the possible techniquesused to remove and recover nutrients from wastewater. Struvite is a valuable fertilizer since it releasesnutrients slowly and has non-burning features owing toits low solubility in water. Struvite formation isobserved at the stoichiometric ratio of 1:1:1 of the ionscomposing struvite according to the following reaction[10,12]:
The success of MAP precipitation depends on twomajor factors: Mg:N:P molar ratio and the pH of the
*Corresponding author. Email: email@example.com
Mg NH PO H O
MgNH H O
+ + -+ + + fi
Y.D. Yilmazel and G.N. Demirer
solution . In a given solution, struvite can form andprecipitate if the product of Mg
ionactivities exceed the ion-activity product at equilibriumor the thermodynamic solubility product . AlthoughH
is not directly involved in the reaction, struviteprecipitation is highly dependent on pH. This is simplydue to changes in the activities of both NH
.Theoretically, solubility of struvite decreases as pHincreases up to a pH level of 9.0. At a pH level above9.0, struvite becomes more soluble as a result ofdecreasing and increasing ion activities of ammonia andphosphate, respectively . However, the pH of mini-mum solubility of struvite may differ owing to changingionic strength and composition of wastewaters. Theminimum solubility pH for struvite precipitationreported by a number of researchers displays a range ofvalues, from 8.0 to 10.7 [10,12]. Struvite precipitation isalso influenced by chemical composition of the waste-water (organic matter, presence of chelating agents,ionic strength), the degree of supersaturation, tempera-ture and the presence of foreign ions such as calcium[810,14].
The struvite precipitation technique has beenapplied to various wastes, such as swine waste ,dairy manure , calf manure , landfill leachate, semiconductor wastewater , slaughterhousewastewaters  and anaerobic digester sidestreams. However, to the best of the authors knowledge,there is only one published work, by Yetilmezsoy andSapci-Zengin , on struvite precipitation from anaer-obically digested poultry manure. In their study, threecombinations of chemicals were tested at different pHlevels, and the performance of the struvite precipitationprocess was evaluated by measuring the remainingchemical oxygen demand (COD), colour and ammoniaconcentrations .
Therefore, in order to fill the gap in the literature,the current study aimed to recover N and P from bothphases of the anaerobically digested and solidliquidseparated effluents of a full-scale poultry manure diges-tion plant. Most of the studies in the literature focusedon the removal/recovery of the readily available nutri-ents in the wastewaters [8,13,16,17]. However, thedissolution of nutrient from the solid phase is the onlyway to recover the highest amount of nutrients, particu-larly phosphorus, from animal wastes. Recently anumber researchers focused on the extraction of thenutrients present in the solid phase of the wastewatersludge [23,24], poultry litter  and piggery wastewa-ter . This study illustrates the feasibility of therecovery of nutrients from the solid phase of anaerobi-cally digested poultry manure by the adoption of anovel phosphorus dissolution process, thereby obtain-ing a phosphorus-enriched liquid phase.
Materials and methods
The wastewater sample was collect