(562ak) Pig Slurry Detoxication and Usage

Letonja, P. - Presenter, Graz University of Technology
Weiß, T., Graz University of Technology
Kunihs, S. A., Graz University of Technology
Groß, C., Graz University of Technology
Siebenhofer, M., Graz University of Technology
Pig slurry is a valuable but unwanted by-product of industrial scale agriculture. The vicinity of industrial livestock farming suffers from odour nuisance during manure discharge. In the low-vegetation period manure discharge (autumn and winter) causes undesirable soil- and groundwater pollution through conversion of ammonia into nitrate.

The increasing consumption of meat does cause a steadily increasing surplus of pig slurry on national and international level. As a rule of thumb a feeding pig has a mean life span of 4 months and it produces about 0.6 m3 of pig slurry with an ammonia content of up to 10000 mg/L.

Detoxication and processing of pig slurry seems to be difficult due to the variety of ingredients, such as ammonia and amines, carboxylic acids, aldehydes, alcohols and hydrogen sulfide based ethers, briefly specified as odour-intensive ingredients. The challenge of finding appropriate technologies lies in the development of suitable treatment steps that can be directly applied at the source (farm) under economically feasible conditions.

The aim of this project was the development of a process for the sustainable solution of the “pig slurry problem” by applying simple technical measures. Through combination of “high impact" technologies, a flexible treatment process for ammonia based nitrogen removal, odor control and effluent management without waste products had to be developed. All products must be suitable for agricultural and horticultural use and the aqueous effluent must at least suffice the quality for irrigation even in low vegetation periods.

The solver for the problem was to neutralize odorous ingredients such as skatol, cresols, phenols, aldehydes and above all butyric acid by alkalizing pig slurry and by stripping ammonia from the liquid slurry to a maximum residual concentration of 100 mg/L and to convert it into ammonium sulfate. Caustic lime and wood ash are recommended for alkalizing large quantities of pig slurry. Ammonium sulfate is a high-quality storable mineral fertilizer for agricultural and horticulture use.

Biochar can completely decolourize the detoxified slurry and it helps improve solid-liquid separation by sedimentation and filtration. The solid residue from phase separation has great potential for use in soil meliorisation. The meanwhile completely transparent filtrate can be used together with the clear run from the sedimentation stage for irrigation/fertilization purposes. In case of necessity the filtrate can be split into a retentate with fertilizer quality and clean permeate by reverse osmosis.

The process, as specified above, was tested in bench scale and in pilot scale and it will go into operation for technical scale validation in autumn 2019. The process is also applicable in cattle manure detoxication and management.