Swine Manure Treatment and Nutrient Concentration by Nanofiltration and Reverse Osmosis
Abstract:The performance of four nanofiltration (NF) and five reverse osmosis (RO) membranes was evaluated during the concentration of manure from a commercial farrow-to-finish swine operation. The raw manure (38.9 g/l total solids (TS)) was prefiltered through diatomaceous earth to yield a liquid fraction containing 12.3 g/l TS and 3.5 g/l total ammonia-N (TAN). Pretreated manure concentration in 24% of the initial volume with the NF membranes produced a permeate that contained between 3.0 and 7.1 g/l TS, and between 1.3 and 2.5 g/l TAN. Thus, NF could not produce water reusable in the barn.
Retention by RO membranes during the concentration of pretreated manure in 46% of the initial volume ranged from 95.2% to 99.6% for TS and from 84.0% to 94.9% for TAN. Total ammonia-N retention tended to decrease with an increase in TAN level in the concentrate and a decrease in operating pressure. With the most selective RO membrane (98.75% salt retention), the permeate collected during manure concentration in 24% of the initial volume contained an average of 372 mg/l TAN and 202 mg/l TS. Permeate quality may not be sufficient for some water reuse applications, such as drinking water for animals or discharge to a water course, but the permeate could be used to fertigate adjacent fields or utilized for cleaning in all-in all-out operations. The concentrate had a high fertilizer value with approximately 8 g/l of TAN and potassium.
Reverse osmosis membranes were also used as a second stage to purify NF and RO permeates. Filtering the NF pretreatment through a RO membrane did not improved final permeate quality compared to a single stage RO filtration, but the operating pressure of the RO stage could be reduced by 25% to 33%. A second filtration of the RO permeate only reduced TAN concentration in the first permeate by about 45%, because of the high pH that developed during the first stage.
With all membranes, initial flux could be recovered by cleaning the system with an alkaline solution after up to 12 days of continuous pretreated manure concentration. However, RO flux decreased considerably during the concentration process due to increased osmotic pressure by the high salt level in the concentrate. Elevated pressures will be required if a high degree of manure concentration were required.
Document Type: Research Article
Publication date: 2008-01-01
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