James Converse, Wisconsin Extension Engineer
There is much interest today in separating manure into liquid and solid streams and partitioning as many of the nutrients in the solid stream as possible. The solid fraction, along with the nutrients that it contains, can be spread on distant fields less expensively than hauling diluted manure and it can also be used as a soil conditioner. A Vincent KP-10 screw separator was used with both dairy and swine manure to determine its ability to separate solids and to concentrate nutrients in the solids stream. At the dairy facility, the manure was scraped to a reception pit that accumulated both manure and milking center wastes. When a lower solids fraction in the input manure was desired for testing purposes, fresh water was added to the reception pit. The manure was agitated and pumped to the screw press. The press was operated with a 0.94-in. perforated screen with 400 and 800 lbs of back pressure and no inlet pressure. At the swine facility, manure that had accumulated in pull-plug pits beneath the slatted floor was conveyed to a reception pit where a pump agitated the manure and pumped it to the separator. The press was operated with a 0.25-in. bar screen with various back and inlet pressures. In this article, the data are not separated for different back pressures and inlet pressures.
For the dairy manure, the influent solids concentration ranged from 1 to 10% solids. The fiber solids output ranged from 26 to 34% dry matter. Solids removal efficiency ranged from 16 to 47% based on the percent solids change between influent and effluent concentration. Nutrient removal (percent of input nutrients in the fiber stream) was directly related to input solids concentration. Table 1 gives an estimate of the nutrient concentration in the solid stream as a function of the input solids concentration. For example, if the input solids (%) to the press was 9%, one could expect that approximately 27% of the phosphorus entering the press would end up in the solid stream and 73% would end up in the liquid stream leaving the press.
For the swine manure, input solids concentration ranged from 1.5 to 5.5% solids. The fiber output ranged from 27 to 35%. Solids removal efficiency ranged from 15 to 30% based on the percent solids change between influent and effluent concentration. Nutrient removal was related to input solids concentration. Table 1 gives an estimate of the nutrient concentration (%) in the solid stream as a function of the input solids concentration.
If your primary goal for solids separation is a relatively dry solids stream (25 to 35% solids), then a screw press is one of the separators that will meet that objective. If your goal is to transfer as many of the nutrients to the solid stream as possible, then using a solid-liquid press might not be the approach to take. Other separators might give somewhat different values than indicated in Table 1, but most separators will be within the ranges given in the table.
Table 1. Approximate percent of nutrients in the solids stream as a function of the input solids concentration into the press.
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1The numbers in this table are approximate and not absolute.
TKN = Total Kjeldahl Nitrogen
NH4+ = Ammonium Nitrogen
TP = Total Phosphorus
K = Potassium
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