Physico-chemical P removal from the liquid fraction of pig manure as an intermediary step in manure processing

Intensive animal farming has resulted in overproduction of manure in parts of the industrialized world. The localized excessive nutrient emission has detrimental effects on both ecology and economy. In response to European guidelines, Flanders (Belgium) has imposed obligations on the agricultural sector to process a portion of the produced animal manure. To achieve the stringent criteria for discharge of processed waste water, overly expensive engineering techniques are currently required (mostly membrane technology). This paper examines the potential of more economic physico-chemical techniques for P-removal from pre-treated liquid animal manure. Two techniques for dephosphatation were performed sequentially: (i) the use of flocculants (FeCl3, FeCl2, FeClSO4, Poly Aluminium Chloride (PAC), Na Aluminate) and subsequently, (ii) the use of substrates to further reduce P-levels by adsorption or precipitation (expanded clay (argex), Fe-oxide powder, clay, calcinated clay, alganite, sand). The P-removal efficiencies obtained in this research are promising to consider implementation of physico-chemical P-removal as an intermediary step in animal manure processing after secondary pre-treatment in an activated sludge reactor and before tertiary treatment.