Changes of Physico–Chemical Properties of Pig Slurry During Storage

This study was aimed to determine changes of the characteristics of raw pig slurry as liquid organic fertilizer at various storage times. A completely randomized design was used in this research. The treatments were storage times, i.e.: 0, 15, 30, 45, and 60 days. Variables observed were loss of the slurry, degree of acidity (pH), electrical conductivity (EC), total solid (TS), volatile solid (VS), total chemical oxygen demand (tCOD), soluble chemical oxygen demand (sCOD), total nitrogen (TN), ammonia-nitrogen (NH3-N), nitrate-nitrogen (NO3-N), total phosphate (TP), and dissolve reactive phosphate (DRP). The results showed that storage time significantly affected all the observed variables, except the concentration of NO3-N and total phosphate content. The pH, TS, VS, DRP, and losses of slurry lost during storage times increased, while EC, TN, NH3-N, tCOD, and sCOD decreased. Physico-chemical properties of slurry during storage times changed, as a result of organic matter breakdown.


INTRODUCTION
There is no doubt that livestock manure has benefi ts as a source of organic fertilizer. Slurry is an important and also heavy metals and pathogens (Araji et al., 2001;Baloda et al., 2001;Barker & Overcash, 2007;Suresh et al., 2009a). Bulluck et al. (2002) measured a greater improvement in physical properties, chemical, and biological soil, and the increased crop production, when applied organic fertilizer compared to chemical fertilizer. The manure is a good nutrient source for crop production. Several studies have shown that utilization of manure in (Zhang et al., 2006), because liquid form has higher niet al., 1986). Liquid manure usually cannot be directly applied to the land, but they must be collected and stored in storage ponds. Application manure as a liquid fertilizer is usually given after harvesting or before planting. The slurry occur microbiological process (Peu et. al., 2006) and mechanical process during storage, which can change physico-chemical characteristics of the liquid manure. Therefore, the objective of this research was to determine the eff ect of storage times on physico-chemical properties of pig slurry.

Materials
The pig slurry was collected from pig houses of University Farm, Animal Environment and Bioengineering Laboratory, Seoul National University, located in Suwon, South Korea. The slurry from storage tank (tank volume around 20,000 l) was mixed (10 min using electric pump) and then 160 l slurry was collected, and they were divided into 16 containers, each container was fi lled 10 l of slurry, then slurry was stored and kept in aerobic condition for 2 mo at the laboratory. The room temperature ranged from 12-18 o C, with relative humidity ranged between 65%-70%.

Sampling and Analysis of Slurry
The physico-chemical properties were observed for 2 mo, and the samples were collected every 15 days. Each period, samples were taken from four containers. The slurry were stirred and followed by sampling. Fifty ml samples were taken from each container periodically, and samples were kept in temperature of 4 o C until they were analyzed.
A loss of slurry was measured by a change of volumes. EC and pH were measured using EC214 conductivity meter (Hana Instruments, Ltd., Sarmeola di aarubano, Italy) and pH meter (Inolab, WTW GmbH, Weilheim, Germany) with a 0.01 pH resolution over the pH range 0-14. TS, VS, tCOD, sCOD, TN, NH 3 -N, NO 3 -N, TP, and DRP were analyzed per standard method for water and waste water (Eaton et al., 2005). The total solid and volatile solid were analyzed by gravity method. The tCOD, sCOD, TN, NH 3 -N, NO 3 -N, TP, and DRP were analyzed using a DR 5000 UV-vis Spectrophotometer (Hach Co., Loveland, Colo) per manufacturer's protocol. Reactor Digestion Method was used to observe tCOD, and sCOD. Persulfate Digestion Method was used to observe TN. Salicylate Method was used to observe NH 3 -N. Chromotropic Acid Method was used to observe NO 3 -N. Acid Persulfate Digestion Method was used to observe TP. Molybdovanadate Method was used to observe DRP.

Statistical Analysis
A completely randomized design was used in this research. Microsoft Offi ce Excel 2007 was used to analyze the experimental data. Data were analyzed by variants analysis, and diff erent mean between treatments were analyzed by Duncans multiple range test (P<0.05). Person product-moment correlation coeffi cient were calculated by choosing bivariate with two tailed option to show the relationship between the observed variables.

RESULTS AND DISCUSSION
Losses of slurry were as a result of evaporation. Mean of losses varied from 0-1.38 l and the rate of losses was 25 ml/day (Table 1). There were increased in losses of slurry to storage times. Mean of losses at each storage times were signifi cantly diff erent. The amount of evaporation was aff ected by humidity, and temperature. Evaporation did not evaporate only water, but also evaporated some compounds, as result of organic materials degradation of slurry. Losses of slurry had a close correlation and aff ected the other properties, such as pH, EC, TS, VS, tCOD, sCOD, TN, NH 3 -N, and DRP ( Table 2).
The EC values ranged from 17.33-19.47 mS/m. The highest EC at 0 day storage times, and the lowest EC at 45 days storage times. There was a change of EC values of slurry. EC values during storage times decreased ( Table 1). The change of EC values showed that there were changes of ion composition in the slurry, because EC described as a result of measurement of ion transfer between the anode and cathode in the solution. EC was normally considered to measure the solubility of salt in the solution (Motsara & Roy, 2008), its correlation to concentration of dissolved ions in a solution (Provolo & Martinez-Suller, 2007). The changes of EC values were as a result of organic compounds degradation and or inorganic compounds to simple molecules or ions. Therefore, EC had a very close relationship with the other properties of slurry ( Table 2). The EC had a positive correlation with the ammonia nitrogen (NH 3 -N), TN, specifi c gravity (SG), TS, VS, fi xed solids (FS), and total dissolved solids (TDS) (Suresh et. al., 2009b).
The pH values ranged from 7.18 to 7.82. The pH slurry signifi cantly increased. The pH increased gradually during storage periods, and moved from neutral to alkali. It was caused by degradation of some intermedislurry pH will become more alkaline in aerobic storage system (Fentonet et al., 1983). On the other hand, increasing acidity would be associated with losses of ammonia. In this study, loss of ammonia continued to rise, because pH of slurry was higher than 7. It is supported by Zhang & Lau (2007) that ammonia emission will increase dramatically, when pH value is higher than 7. Furthermore, there were negative correlation between pH and NH 3 -N concentration of slurry (Table 2). It means that pH was aff ected by ammonia emission to atmosphere. When pH was low, losses of ammonia from slurry can be reduced.
The mean of TS concentration varied from 16.65-20.21 g/l. The mean of VS ranged from 10.66 to 12.99 g/l. Concentration of TS and VS increased during storage times (Table 1). Increased concentration of TS and VS in slurry was infl uenced by the loss of water due to evaporation. Although there were degradation of tion of TS and VS, because the rate of water loss through evaporation was greater than the rate of degradation of organic material. Beside that, TS concentrations aff ected and had a correlation to the other properties such as pH, EC, VS, tCOD, sCOD, TN, NH 3 -N, DRP, and losses of slurry (Table 2).
The mean of tCOD ranged from 25.50-29.35 g/l, while the mean of sCOD varied from 12.75 to 18.70 g/l (Table 1). There were decreased of tCOD and sCOD during storage periods. Decreasing of tCOD were signifi cantly diff erent at 0-15 days storage times and 30 to 45 days storage times, while 15 to 30 days and 45 to 60 days were not signifi cant change. The content of soluble COD decreased during increasing storage times. The COD described the organic substrate in the solution. The tCOD and sCOD decreased during storage periods Table 2. Pearson correlation between the observed variables Note: *= P<0.05, **= P<0.01. EC= electrical conductivity, TS= total solid, VS= volatile solid, tCOD= total chemical oxygen demand, sCOD= soluble chemical oxygen demand, TN= total nitrogen, NH 3 -N= ammonium nitrogen, NO 3 -N= nitrate nitrogen, TP= total phosphate, DRP= dissolve reactive phosphate, LS= losses of slurry. showed there was degradation of COD, or occurred degradation of organic material. At storage periods, there were activity of microorganisms to break down organic found in slurry are carbohydrates, fat, protein, and NPN.
Carbohydrates and fats will be released into the atmosphere in gaseous form, while protein and NPN will be degraded to be simple nitrogen molecules, namely NH 3 , N 2 , N 2 et al., 2007). Furthermore, ammonia is a gas that indirectly aff ects to the enhanced greenhouse eff ect through physical and chemical processes in the atmosphere and soil (Seidl, 1999). Changed of sCOD could be used as indicator for other properties, because sCOD have correlation to pH, EC, TS, VS, tCOD, NH 3 -N, DRP, and losses of slurry ( Table 2).
The concentration of TN ranged from 2.49 to 3.80 g/l ( Table 1). The TN concentration during storage periods decreased. The mean concentrations of TN at 60 days were signifi cantly diff erent compared to 0-15 days storage times. The decrease was due to nitrogen emissions to the atmosphere. These gases were products from decomposition of urine and undigested proteins in slurry.
The concentration of NH 3 -N varied from 1.03 to 1.40 g/l (Table 1). It trends to decrease when storage times increased. Decreasing of NH 3 -N concentration indicated losses of nitrogen in the ammonia form, ammonia in the solution will be evaporated easier. It is supported by many studies. Approximately 50% losses of nitrogen in slurry are ammonia (Harper et al., 2000), the others are N 2 , and only a small portion are N 2 release of ammonia from the manure is a slow process which governed by factors as ammonia concentration, (Aarnink & Verstegen, 2007). The ammonium ion (NH 4 ) will be converted to ammonia (NH 3 ) when the degree of acidity increased (Karakashev et al., 2008). In addition, emission of NH 3 will be higher if there were increased of temperature and ammonium ion concentration, and the wind will accelerate the emission of NH 3 into the atmosphere.
The concentration of NO 3 -N ranged from 0.64 to 0.77 g/l (Table 1). There were not diff erent of NO 3 -N concentration, it means that N-NO 3 concentrations were not aff ected by storage times. It indicated that nitrifi cation process is equal to denitrifi cation process. Nitrate is the end product of nitrifi cation process, converse of ammonium to nitrate by bacterial activity. Nitrate can be conversed to NO, N 2 O, and N 2 through denitrifi cation process. Moreover, NO 3 -N concentration did not have correlation to other properties (Table 2) The mean concentration of TP varied from 0.41 to 0.45 g/l (Table 1). There were no diff erent of TP concentration, it means that TP concentrations were not aff ected by storage times. Losses of phosphates during storage period by evaporation are extremely rare, because losses of phosphates occur more frequently when slurry is applied to land, through the mechanism of run off and leaching. Losses of phosphates when applied as organic fertilizer has been widely studied (Tabbara, 2003;Daverede et al., 2004).
The mean concentration of DRP varied between from 0.28 to 0.40 g/l ( Table 1). The DRP concentration increased during storage times. The concentration of DRP dramatically increased after 15 days, increased almost 100 mg/l. During storage, there was a change of organic forms (Fontenot et al., 1983). Although total phosphates concentration did not change, but the composition of phosphates changed, namely from organic phosphate to inorganic phosphates through decomposition process by microorganism. In this study, comparison TP concentration to DRP concentration ranged from 66% to 89%. According to Sharpley and Moyer (2000), pig slurry contains 80%-90% DRP from TP. The increasing of DRP concentration will increase the availability of phosphor for plant nutrient, while phosphor will be the easiest to uptake by plant. If it is applied to agricultural lands in the form of animal slurry has the potential source of pollution on surface waters, leading to eutrophication.

CONCLUSION
Physico-chemical properties of pig slurry changed during storage. Losses of slurry, pH, TS, VS, and DRP concentration increased, but EC, tCOD, sCOD, TN, and NH 3 -N concentration decreased during storage period, while concentration of NO 3 -N and TP did not change. Losses of slurry, sCOD and NH 3 -N concentration had a close correlation to other properties, except to NO 3 -N, and TP. The pig slurry as a source of liquid organic fertilizer must be treated to minimize nutrient loss and pollution.