Progress 10/01/01 to 09/30/06
Outputs
SOLUBLE PHOSPHORUS EXTRACTION AND RECOVERY FROM ANAEROBICALLY DIGESTED DAIRY MANURE: Effluent samples were collected from six on-farm anaerobic digesters from the following five dairy operations in Wisconsin: Double S, Gordondale, Stencil, Tinedale, and Wholesome. Wholesome dairy has two digesters (Wholesome-East and Wholesome-West) while the other operations have only one digester. All effluent samples, with the exception of Double S, were obtained directly downstream of the digesters. Since the digester at Double S has no direct access to the effluent, the sample was collected downstream of the solids separator. Average water-extractable phosphorus (WEP) of these digester effluents was comparable: 2.9, 2.9, 2.8, 2.8, 2.4, and 2.5 g/kg for Double S, Gordondale, Stencil, Tinedale, Wholesome-East, and Wholesome-West, respectively. However, differences were observed in the ratio of WEP to total P (TP) (i.e., WEP/TP ratio) and it was 36.9, 26.5, 43.1, 35.6, 32.4, and 38.2
% for the corresponding samples. The lowest and highest WEP/TP ratio was for samples from Gordondale and Stencil farms, respectively. Phosphorus fractionation of Gordondale effluent was performed using a Retsch automated sieve shaker. Six sieves with the following opening sizes were used: 1,000, 500, 250, 106, 53, and 25 um. Percentage of P retained by each sieve was 34.8 % (1,000 um), 21.6 % (500 um), 11.0 % (250 um), 5.4 % (106 um), 5.2 % (53 um), and 22.0 % (25 um). Phosphorus in anaerobically-digested effluent was partitioned into two major size fractions: 67.4 and 22 % of P in size ranges of > 250 and 25-53 um, respectively. Digestate sample (liquid portion from the mechanical separator) was collected from the downstream portion of anaerobic digester at Gordondale and was used for struvite recovery experiments in spring 2006. The digestate contained a total solids level of 3.5% with most of the P distributed in the finer-sized fractions (< 53 um). The digestate was directly
subjected to chemical treatment for P recovery. Sodium hydroxide and magnesium chloride were used to promote formation of large settleable flocs containing P. Our results indicate that addition of 1-2 g of magnesium/g of manure P and 3.2 g of NaOH/L of digestate was capable of concentrating as much as 70% of P from the liquid to the sludge fraction, with a minimum settling period of 4 hours. Furthermore, this treatment sequence resulted in lowering the WEP fraction as compared to that in untreated digestate. Application of manure with low WEP/TP ratio to agricultural soils would reduce P availability in runoff.
Impacts
We expect the treatment system (tested above) will produce solids with low levels of water-extractable phosphorus (P) and recover P as struvite with minimal Mg amendment. The separated solids can be recycled on-farm for bedding and other purposes. Phosphorus condensed in struvite can not only be transported off-farm, as a slow-release fertilizer, but also used as a raw material in P industry.
Publications
- Gungor, K. and K.G. Karthikeyan. 2007. Phosphorus Forms and Extractability in Dairy Manure: A Case-study for Wisconsin On-farm Anaerobic Digesters. Bioresource Technology (in press).
- Gungor, K., and K.G. Karthikeyan. 2005. Influence of Anaerobic Digestion on Dairy Manure Phosphorus Extractability. Transactions ASABE. 48:1497-1507.
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Progress 01/01/05 to 12/31/05
Outputs
The effect of anaerobic digestion on phosphorus (P) forms and water P extractability was investigated using dairy manure samples from six full-scale on-farm anaerobic digesters in Wisconsin, USA. Total dissolved P (TDP) constituted (on an average) 12% and 7% of total P (TP) in the samples influent to and effluent from anaerobic digesters, respectively. Dissolved unreactive P (DUP), comprising polyphosphates and organic P, dominated the dissolved P component in both the influent and effluent. In most cases it appeared that the fraction of DUP mineralized during anaerobic digestion became subsequently associated with particulate-bound solids. Geochemical equilibrium modeling with Mineql+ indicated that dicalcium phosphate dihydrate, dicalcium phosphate anhydrous, octacalcium phosphate , newberryite, and struvite were the probable solid phases in both the digester influent and effluent samples. The water-extractable P (WEP) fraction in undigested manure ranged from 45 to
70 % of TP, which reduced substantially after anaerobic digestion to 25 to 45 % of TP. Anaerobic digestion of dairy manure appears capable of reducing the fraction of P that is immediately available by increasing the stability of the solid phases controlling P solubility. Additional research is necessary to specifically examine the mechanism causing an increase in P solid phase stability after anaerobic digestion. This mechanism could be exploited for the design of on-farm anaerobic digestion systems to maximize P recovery from animal manures.
Impacts
Design of anaerobic digestion systems for animal manure can be suitably modified to maximize subsequent P recovery from manure.
Publications
- Gungor, K., and Karthikeyan, K.G. 2006. Phosphorus Forms and Extractability of Dairy Manure: A Case Study for Wisconsin On-farm Anaerobic Digesters. Bioresource Technology (in review).
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Progress 01/01/04 to 12/31/04
Outputs
Anaerobic digestion is becoming an increasingly attractive option to treat dairy manure, since it offers several benefits including conversion of organic solids to biogas (renewable energy), odor mitigation, and pathogen reduction. We feel that conventional manure handling systems will be replaced in future with integrated units comprising multiple processes (e.g., a combination of physical/chemical/biological treatment). Since the ultimate disposal of treated/untreated manure involves land application, it is critical to understand P dynamics after anaerobic digestion. We investigated the effect of different inoculum-to-substrate ratios (ISRs) on P extractability from anaerobically treated manure. Dairy manure (substrate) and anaerobically digested dairy manure (inoculum) were collected from an on-farm anaerobic digester. High ISR (HIS, with ISR = 2.0) and low ISR (LIS, with ISR = 0.3) samples were prepared on a volatile solids (VS) basis. These samples were subjected
to mesophilic anaerobic digestion in batch reactors without mixing for 120 d. Total solids and VS removal were higher in at LIS system compared to HIS. Serial and repeated extraction methods were used to characterize P extractability. De-ionized (DI) water was used as extractants in the serial extraction method with extractant-to-manure ratios (EMR) ranging from 3 to 127. For repeated extraction, manure was extracted six times with DI water (EMR = 3). While anaerobic treatment decreased water-extractable P (WEP) in LIS extracts at EMR values of 3 and 7 by 28 % and 24 %, respectively, a significant increase (40%) in WEP occurred at an EMR of 3 at HIS. WEP in all other serial extracts of treated manure was higher regardless of ISR and EMR. Extractability of P increased sharply up to the third extraction step after which it leveled off. The effectiveness of anaerobic digestion at LIS to reduce P extractability was also observed up to the second extraction step. In contrast, the digested
manure always produced higher WEP levels for the HIS system. Our preliminary results indicate that, depending on the ISR used, anaerobic digestion of dairy manure can increase or decrease manure P extractability and, hence, its availability in runoff.
Impacts
Concentration of animal feeding operations and use of inappropriate manure management practices have exacerbated degradation of impaired water bodies. Conventional manure management is not sufficient to address this problem. Integrated manure treatment systems involving a combination of physical-chemical and biological treatment trains might be required for an environmentally sound solution. As one of the biological treatment processes, anaerobic digestion can be a part of this integrated approach. Not much information is available on the effect of this treatment method on phosphorus dynamics, which needs to be understood as manure nutrient management is a fundamental issue in agricultural non-point source pollution control.
Publications
- Gungor, K., and K.G. Karthikeyan. 2004. Inorganic Phosphorus Forms and Extractability in Anaerobically Digested Dairy Manure. ASAE Meeting Paper No. 044077. 2004 ASAE Annual Meeting. ASAE. St. Joseph, MI.
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Progress 01/01/03 to 12/31/03
Outputs
Chemical treatment of animal manure with Al, Fe, and Ca salts appears capable of concentrating P in a smaller volume, thereby providing increased manure management options. However, very little information is available on the fate of nutrients in soils receiving chemically treated manure. An incubation study was conducted with 3 soils (I, II, and III with 12, 66, and 94 mg/kg Bray-1 P), 4 manure treatments (1 untreated; 3 chemically [alum - Al; ferric chloride - Fe, lime - Ca] treated), at 2 rates (25 and 50 kg P/ha), and a control (no manure). Sub-samples were analyzed for water-extractable NO3- and NO2-, K+ -exchangeable NH4+ and water-extractable P (WEP) after each incubation time (1 day, 1 & 2 weeks, 1, 3 & 6months, and 1 year). Nitrate release was controlled by treatment type (untreated > Al-treated > Fe-treated > Ca-treated > control) and manure application rate and increased sharply between 1 day and 1 or 2 weeks and then slowly at longer incubation periods. In
contrast, K+ -exchangeable NH4+ exhibited a sharp decrease during the first week and then remained relatively constant for up to 1 year. WEP increased when soils received untreated or Ca-treated manure with the magnitude being proportional to the rate of manure (i.e., P) applied. WEP, however, decreased (compared to control) for soils II and III (high Bray-1 P) or slightly increased for soil I (low Bray-1 P) with application of Al or Fe-treated manure. WEP decreased sharply between 1 day and 1 or 2 weeks incubation and then remained relatively constant or increased slightly up to 1 year depending on treatment and soil type. Addition of Al or Fe treated manure decreases P solubility, with the effect more pronounced in soils with high background P.
Impacts
This study attempts to bridge the gaps between our knowledge of chemical treatment systems for dairy manure (intended to remove P and solids) and the ultimate fate of P when the treated manure is land applied. Our results in conjunction with those from chemical treatment studies will help select optimum formulations of chemicals (coagulants and flocculants) that can maximize concentration of solids/nutrients in dairy manure. Our findings are critical for designing any chemical treatment and land application systems, which will provide increased options to manage dairy manure.
Publications
- Kalbasi, M. and K.G. Karthikeyan. 2003. Nutrient Dynamics in Soils Receiving Chemically Treated Dairy Manure. In Robert Burns (ed.) Proceedings of the Ninth International Symposium on Animal, Agricultural and Food Processing Wastes, 12-15 October 2003, Raleigh, NC, p 655-665.
- Kalbasi, M. and K.G. Karthikeyan. 2003. Phosphorus Dynamics in Soils Receiving Chemically Treated Dairy Manure. Wisconsin Fertilizer, Aglime and Pest Management Conference, Jan 21-23, 2003, Madison WI.
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Progress 01/01/02 to 12/31/02
Outputs
Flushed raw dairy manure (influent)and effluent from a screw press were placed in separate 15 cm diameter settling columns with a working volume of 12 liters. Settling times ranged from 4 hrs to 49 days. The objective of the study was to determine the % of the nutrients and solids that could be concentrated into a small volume by settling. The results of the study are based on % of the nutrients or solids that were placed in the column. The ammonia and potassium were unaffected by settling and remained essentially the same concentration throughout the column. Approximately 30% of the total nitrogen was concentrated in the bottom 25% of the volume. After 4 hrs approximately 50% of the total phosphorus and solids were concentrated in the bottom 25% of the volume. After 49 days approximately 75% of the total phosphorus and 58% of the solids were concentrated in the bottom 25%. The N:P:K ratio is affected by settling with longer settling times having a greater effect on
settling as a higher percentage of P settles out over time than does N and K. Passing the manure through a solid/liquid separator will remove some of the nutrients and will also minimize flotation of solids during settling.
Impacts
This study shows that long term settling can significantly remove upwards of 75% of the phosphorus from 75% of the manure stream. Settling after solids/liquid separation could be incorporated into the manure handling stream for flushed manure systems to remove additional phosphorus which would impact how the manure handling system is designed.
Publications
- Converse, J.C. and K.G. Karthikeyan. 2002. Nutrient and Solids Separation of Flushed Dairy Manure by Settling. Paper presented at the 2002 ASAE Annual International Meeting/CIGR XVth World Congress. Chicago. ASAE St. Joseph, MI
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