Pig Slurry Solids Research Articles

Selection of Mediterranean plants biomass for the composting of pig slurry solids based on the heat production during aerobic degradation

Heat recovery from composting processes and its use as a source of bioenergy have come into prominence in recent years. In this study, the selection of an adequate bulking agent for the composting of the solid fraction of pig slurry has been based on the heat produced by the microbial activity during aerobic degradation of the organic matter. Residues of five plant species typical of the Mediterranean area were mixed with the solid fraction of pig slurry, as bulking agents. The residues were: the prunings of three common cultivated tree species (orange, palm, and olive) and the biomass of two herbaceous species (milk thistle and sunflower). Self-heating tests were run for 18 days in thermally insulated laboratory-scale reactors; the energy released as heat was calculated from the temperature increase inside the reactors. The mixtures were sampled at the beginning and end of the experiment, and the microbial stability was evaluated by aerobic respiration tests. The heat energy produced was highest in the mixture with milk thistle (18.3 ± 1.78 MJ kg−1 of total solids -TS), followed by that with orange tree prunings (16.0 ± 1.094 MJ kg−1 TS), and was lowest with olive tree prunings (6.3 ± 0.23 MJ kg−1 TS). The microbial biodegradability of the mixtures and the physico-chemical characteristics (mainly the C/N ratio, cellulose concentration, and density) of the different bulking agents controlled the heat energy produced. The orange tree prunings were considered the most suitable bulking agent for composting of pig slurry solids as they showed high degradability and energy recovery potential.

Composts Produced From Pig Slurry Solids: Nutrient Efficiency and N-Leaching Risks in Amended Soils

Composts were prepared from the solid fraction of pig slurry (SPS) by mixing with cotton gin waste (CGW) in two different proportions. The aim was to assess the fertilizer value of the two composts and to evaluate potential pollution risks due to the heavy metal (Cu and Zn) concentrations in the composts and the nitrate leaching following their soil application. For this, a pot trial using Italian ryegrass (Lolium multiflorum Lam.) as a test plant was run in a glasshouse. Two composts, A and B, prepared with SPS:CGW ratios of 4:3 and 3:4 (v:v), respectively (OM 63 and 57 %, TN 36.1 and 32.7, and TP 15.3 and 10.8 g kg-1 in A and B, respectively), were applied to a sandy loam soil at two doses based on the N supplied (D1: 360 mg TN pot-1, equivalent to 52 kg N ha-1, and D2: 720 mg TN pot-1). They were compared with a soluble mineral fertilizer (3.62 g pot-1 of N:P:K 10:10:10; providing 360 mg N pot-1); unfertilized control soil was also tested. The potential risk of nitrate-N leaching in the soil after two simulated intense rainfall events was evaluated. The experiment was carried out in double-layer pots, which allowed the collection of leachates. Both composts were able to increase plant biomass production and soil TN and available-P with respect to the control; available Cu and Zn in the soil did not increase significantly with respect to the control soil and mineral fertilizer treatment, although N deficiency limited plant growth at harvests 2 and 3. The compost prepared with a higher proportion of SPS (A) was more efficient for N fertilization (relative agronomic efficiency: 38.1-47.6 %; nitrogen use efficiency: 34.1-41.9 % of TN), due to its greater inorganic-N concentration. To obtain high P and K efficiencies application rates based on compost TN are recommended, which also prevent Cu and Zn soil enrichment. Nitrate leaching was very low in all treatments (<0.5 % of TN applied). Therefore, both composts can be used as organic fertilizers in the partial substitution of mineral fertilizers, without a significant nitrate leaching risk.

Influence of storage on methane yields of separated pig slurry solids

Biogas production from separated pig slurry solids is more profitable than using untreated raw slurry because there is a higher CH4 potential per unit fresh matter. However, logistics needs to be optimized. A stable storage without losing the high biogas potential could enable deliveries on demand. Self-heating and CH4 yields of aerobically and anaerobically stored pig slurry solids were analysed and compared. The aerobic storages had run times of 33 and 44 days. Anaerobic storage took 7, 23 and 35 weeks. Anaerobically stored solids show no self-heating and produce CH4 yields of up to 188 L kg−1 ODM. This is over twice as much as the aerobically stored solids produce and about the same CH4 yield produced by freshly separated solids. Additionally, a mass loss occurs under aerobic storage that reduces the methane yield of the original material too.

A novel challenge test incorporating irradiation (60Co) of compost sub-samples to validate thermal lethality towards pathogenic bacteria

Maturing compost heaps normally attaining temperatures ranging from 55 to 65°C is generally regarded to conform to recommended biological risks and sanitation standards for composts stipulated by either EU or US-EPA. Composted products derived from animal sources are further required by EU biohazard safety regulatory legislation that such composts either attain 70°C for over 3h during maturation or via treatment at 70°C for 1h before being considered for dispensation on land. The setting of the upper limit of thermal lethality at 70°C/1h for achieving biosecurity of the animal waste composted products (e.g. pelleted fertilizer formulations) is not properly substantiated by specific validation tests, comprising a ‘wipe-out’ step (usually via autoclaving) followed by inoculation of a prescribed bacterium, exposure to 70°C/1h and the lethality determined. Pelleted formulations of composts are not amenable for wet methods (autoclaving) for wipe-out sterilization step as this is detrimental to the pellet and compromises sample integrity. This study describes a laboratory method involving the employment of (60Co) irradiation ‘wipe-out’ step to: (a) compost sub-samples drawn from compost formulation heaps and (b) pelleted products derived from composted animal products while determining the thermal lethality of a given time/temperature (70°C/1h) treatment process and by challenging the irradiated sample (not just with one bacterium but), out with 10 potential food-poisoning organisms from the bacterial genera (Campylobacter, Escherichia, Listeria, Salmonella, Yersinia) frequently detected in pig and poultry farm wastes. This challenge test on compost sub-samples can be a useful intervention ploy for ‘inspection and validation’ technique for composters during the compost maturity process, whose attainment of temperatures of 55–65°C is presumed sufficient for attainment of sanitation. Stringent measures are further required by law for composted products arising from rural industrialists producing pelleted fertilizers from re-composted animal agriculture wastes comprising pig slurry solids, poultry litter and spent mushroom compost, which carry residual food-borne pathogens with implications to the food chain including humans. Environmentally, sustainable means of recycling farm wastes require that final composted products are free of pathogens in compliance with environmental safety legislation before their release to the market. This test developed provides a science-based risk characterization tool for sustainably managing environmental safety by ‘validating’ thermal lethality of a given composting process or their derivatives achieved without compromising the sample integrity or ambiguity attached to microbiological validation involving steam sterilization or autoclaving procedures and helps audit the resurgent bacterial populations from surviving non-pathogenic organisms in the end-products of animal waste compost formulations.

Pelleted organo-mineral fertilisers from composted pig slurry solids, animal wastes and spent mushroom compost for amenity grasslands

In Ireland, conversion of biodegradable farm wastes such as pig manure spent mushroom compost and poultry litter wastes to pelletised fertilisers is a desirable option for farmers. In this paper, results obtained from the composting of pig waste solids (20% w/w) blended with other locally available biodegradable wastes comprising poultry litter (26% w/w), spent mushroom compost (26% w/w), cocoa husks (18% w/w) and moistened shredded paper (10% w/w) are presented. The resulting 6-mo old ‘mature’ composts had a nutrient content of 2.3% total N, 1.6% P and 3.1% K, too ‘low’ for direct use as an agricultural fertiliser. Formulations incorporating dried blood or feather meal amendments enriched the organic N-content, reduced the moisture in mature compost mixtures and aided the granulation process. Inclusion of mineral supplements viz., sulphate of ammonia, rock phosphate and sulphate of potash, yielded slow release fertilisers with nutrient N:P:K ratios of 10:3:6 and 3:5:10 that were suited for amenity grasslands such as golf courses for spring or summer application and autumn dressing, respectively. Rigorous microbiological tests carried out throughout the composting, processing and pelletising phases indicated that the formulated organo-mineral fertilisers were free of vegetative bacterial pathogens.

Effect of Pig Slurry Solids on Aeration Efficiency and Odour Generation

Two laboratory-scale experiments were carried out in this study to determine the effect of slurry solids content on aeration efficiency and the odour generation potential for the treated slurry during post-aeration storage. Pig slurry with four total solids levels (0·5, 1·0, 2·0, and 4·0%) were used for both experiments. In the first experiment, the slurry was aerated and the oxygen transfer coefficient (OTC) for each solids level was determined. When the solids content increased from 0·5 to 4·0%, a reduction in OTC from about 0·59 to 0·15 min−1 was observed. However, no statistically significant differences in OTC were found between slurry with a 0·5% and 1·0% total solids content and between slurry with a 2·0% and 4·0% total solids content, while the difference was significant between these two solids groups. In addition to OTC, the oxygen-holding capacity of the aerated manure decreased significantly with increasing slurry solids content. In the second experiment, slurry with the same four solids categories was contained in Plexiglas columns and aerated at a dissolved oxygen level of 1 mg l−1 for 15 days. After aeration, the slurry was left in the columns to simulate long-term storage (180 days). The removal rates of volatile fatty acids (VFA), an odour indicator, by aeration were 98, 96, 67, and 31% for total solids content of 0·5, 1·0, 2·0, and 4·0%, respectively. During the entire storage period, the VFA concentrations for slurry with solids contents of 0·5% and 1·0% were consistently lower than 230 mg l−1, indicating that the chance for offensive odour to return was moderate. In contrast, the slurry in the two upper solids categories showed VFA levels consistently higher than 230 mg l−1 throughout the 180 day storage period. At the end of the storage, the odour detection threshold values were 531, 708, 812, and 1627 for slurry with solids content from 0·5 to 4·0%.

Evolution of temperature and chemical parameters during composting of the pig slurry solid fraction amended with natural zeolite

A 3-month experiment was conducted at a 300 kg scale to observe decomposition processes in pig slurry solids amended with two different doses of natural Slovak zeolite–clinoptilolite (substrates S1 and S2, 1% and 2% of zeolite by weight, respectively) in comparison with the control (unamended solids). The experimental and control substrates were stored outdoors in sheltered static piles at ambient temperatures ranging from 8.0 to 34.7 °C. The solid fraction (SF) of pig slurry was obtained by separation on vibration sieves prior to slurry treatment with activated sludge. The initial water content of the SF was 77.1% and no water was added to the piles during the storage. The temperature in the core of the piles was recorded throughout the experiment. By day 3 and 5 of storage (1% and 2% zeolite, resp.), the temperature in the substrates S1 and S2 exceeded 55 °C and remained above this level for 15 days while the highest temperature recorded in the control during the experiment was 29.8 °C. Samples from the core of the piles were taken periodically to determine pH, dry matter at 105 °C (DM), ash (550° C/4 h), ammonia nitrogen (N-NH 4 +), nitrate nitrogen (N-NO 3 −), total nitrogen (N t), total phosphorus (P t); total organic carbon (TOC) was computed. The results showed that pH levels in S1 and S2 remained below that in the control for most of the thermophilic stage. This may be related to water-soluble ammonia and the affinity of zeolites to ammonium ions. A significant decrease in the level of ammonia nitrogen in water extracts from S1 and S2 was observed between days 5 and 35 in comparison with the control. The values of ash also differed and corresponded to the intensity of the decomposition processes in the respective substrates.

Production of Environmentally Safe and Sustainable Compost-based Fertilizer Products from Horticultural and Farm Wastes

The EU Regional Draft Waste Management Plan (1999-2004) identified pig slurry (501,590 tonnes), poultry manure (217,110 tonnes) and spent mushroom compost (221,665 tonnes) as the main contributors to the 3.5 million tonnes of waste generated annually in Ireland. Current legislative restrictions prevent pig wastes from intensive pig units and horticultural wastes mainly spent compost produced in mushroom farms being disposed via landspreading due to pollution threat from nutrient run-off and the health hazards due to animal and human risk pathogen contents in wastes. Composting is a world-wide popular option for environmentally sustainable means of recycling farm wastes. In Ireland, profitable conversion of farm wastes such as pig slurry solids and spent mushroom compost has not yet been fully explored for their economic viability as `green' fertilizers. In this study, we produced pelleted formulations of the composted pig waste solids, (20%) blended with spent mushroom compost (26%), turkey litter (26%) cocoa husks (18%) and shredded paper (10%) to an environmentally safe, organic-based fertiliser resulting in N:P:K = 3:5:10, ideally suitable for use on amenity grassland such as golf course fairways and greens in Ireland, wherein spring and summer fertilizers with slow release of nutrients would aid an even growth of grass. We describe the composting methods used, processing technology developed and additional amendments such as dried blood or feather meal that were used during the pelletisation operation yielding specific N:P:K target ratios from the pig manure and spent compost wastes. We also report on the rigorous microbiological tests carried out throughout the composting phase and ascertained the pathogen-free status of the final pelletised fertilser products.

Effect of natural zeolite (clinoptilolite) on microbial decomposition processes in stored pig-slurry solids.

The solid fraction (SF) of pig slurry obtained in the first stage of aerobic slurry treatment was amended with 1 and 2% zeolite (clinoptilolite) and stored for 12 weeks under anaerobic conditions or with turning after 3 and 6 weeks of storage. In addition to that SF was mixed with 2% zeolite, 50% (V/V) sawdust, and both sawdust and zeolite, and stored for 6 weeks with turning after 1 and 3 weeks. Plate counts of psychrophilic, mesophilic, coliform and fecal coliform bacteria, determined during the storage, corresponded to the development of temperature in the core of the substrates. An effect of amendment of SF with zeolite and sawdust on plate counts of selected bacteria was observed, dependent on the zeolite dose. The thermophilic phase was not reached in any of the investigated substrates. The populations of fecal coliforms in the substrate amended with 1% zeolite and turned after 3 and 6 weeks decreased after 11 weeks down to 500 CFU/g substrate.

Composition andin saccoDegradability of Variously Treated Pig Slurry Solids before and after Anaerobic Digestion

Abstract Flachowsky, G., Richter, G. H. and Löhnert, H.J. 1995. Composition and in sacco degradability of variously treated pig slurry solids before and after anaerobic digestion. J. AppL Anim. Res., 7: 161–168. The fresh and digested pig slurry was separated into a solid and liquid phase by centrifugation. The solids of the slurry (fresh and digested) were treated with urea and I or NaOH and used for the estimation of chemical composition and dry matter degradability (DMD). Anaerobic digestion did not significantly influence chemical composition except iron content. The DMD of anaerobically—digested solids was significantly lower (34.8%) than that of the influent material (48%). Chemical treatment of solids from the influent increased DMD from 48.0 to 54.5 (2% urea), 60.2 (2% NaOH) and 62.0% (2% urea and NaOH each); DMD of effluent was increased from 34.8 to 46.4, 49.4 and 51.3%, respectively. Pig slurry solids from the effluent of anaerobic digesters contain low energy for ruminants and should primarily be used as manure.

Composition and digestibility of untreated and chemically treated animal excreta for ruminants—A review

The paper reports on the crude nutrient content and the mineral profile, as well as the apparent digestibility by ruminants, of faeces of poultry, pigs and cattle, poultry litter and solid matter of poultry, pig and cattle slurries. The second part of the paper deals with chemical treatment of pig and cattle slurry solids with NaOH, KOH and urea. Nutrient and mineral content as well as digestibility of animal excreta are greatly influenced by species, age and type of feeding, the bedding material used and the method of solid-liquid separation of slurries. The digestibility of poultry excreta is higher than that of pig waste. Cattle faeces are unsuitable as feeds even after chemical treatment. In sacco degradability, apparent digestibility, energy content and intake of pig slurry solids were increased by treatment with urea, NaOH and KOH. Level of chemicals used and temperature influenced the effect of treatment. Wet pig-slurry solids may be preserved with urea.

Feed value and feeding of wastelage made from distillers grain solubles, pig slurry solids and ground straw treated with urea and NaOH

Urea at five levels (0, 1, 2, 4 and 6%) and NaOH at two levels (2 and 4% of dry matter to each of 2 and 4% urea level) were added to a mixture consisting of seven parts distillers grain solubles, two parts pressed pig slurry solids and one part ground wheat straw, on a fresh weight basis. After a fermentation period of 42 days at ambient temperature in 100-litre capacity silos, the pH dropped in the unsupplemented wastelage (3·90), but it increased after urea and NaOH supplementation (up to 7·14). Ammonia and acetate concentrations in wastelage were enhanced with urea addition. Increase of acetate and butyrate concentration was observed when NaOH was added. In sacco degradability increased from 49·0% (untreated sample) to 67·0% when 2% urea and 4% NaOH were added. The rumen dry matter degradability of wastelages was significantly higher when sheep consumed a diet rich in roughages (57·5%) rather than a concentrate ration (50·1%). Sheep consumed about 1 kg dry matter daily when unsupplemented or when 1% urea-added wastelage was fed. Higher levels of chemicals decreased dry-matter intake. Chemically-treated wastelage replaced about a half of wilted grass silage without any negative effect on daily weight gain in short-term feeding experiment with growing bulls.

Digestibility and beef performance after feeding NaOH- or KOH-treated pig wastes

Pig slurry solids were treated with NaOH or KOH. The effect of both alkalis has been evaluated by measuring in vitro and in vivo digestibility, solid intake of bulls and two long-term feeding experiments (273 and 263 days) with dairy beef cattle. The addition of 1% NaOH or KOH increased the in vitro digestibility of organic matter by 1.4 or 0.9 percentage units and 1 mole equivalent caused an increase of digestibility by 4.9 or 5.0 units, respectively. The in vivo digestibility was increased by 3.4 or 2.6 percentage units per 1% NaOH or KOH and by 14 and 15 percentage units per mole equivalent. Bulls consumed significantly ( P < 0.05) more NaOH- or KOH-treated by-products, compared with untreated material, if they could choose freely between the solids. There were no significant differences ( P < 0.05) between NaOH- or KOH-treated pig wastes with regard to dry matter intake and daily weight gain of bulls. More than 70% total dry matter intake consisted of pig wastes. Animal performance was not improved by using a mixture of NaOH and KOH, compared with NaOH or KOH separately. The effect of KOH is basically equal to that of NaOH in treatment of the by-products on an equimolar basis. About 40% more KOH, by weight, would be required to give equal results in digestibility and animal performance.

Rumen dry Matter Degradability of Various Pig Faeces and Chemically Treated Pig Slurry Solids

Rumen dry Matter Degradability of Various Pig Faeces and Chemically Treated Pig Slurry Solids