A collaboration between scientists at Michigan State University and McLanahan Corp has seen the development of a system that takes manure, such as dairy effluent, and cleans it so the remaining liquid is good enough for stock to drink.
MSU's Associate Prof Steven Safferman said the system could have applications for New Zealand dairying.
Prof Safferman and colleague Emeritus Prof Bill Bickert, using graduate research by former MSU student Jim Wallace, now of
McLanahan Corp, have been researching anaerobic digestion as part of a comprehensive nutrient management process.
The system uses an anaerobic digester (a machine that uses micro-organisms to break down biodegradable waste in the absence of oxygen),
which is coupled with an ultra-filtration, air-stripping and reverse osmosis system.
''The process takes a complex waste with mixed pollutants and separates each resource out so it can be effectively and efficiently managed,'' Prof Safferman said. Ultra-filtration was used to separate larger particles from the bulk liquid, phosphorus and organic nitrogen being primarily contained in the material that did not pass though the filter.
''Air stripping transfers the ammonia in the bulk fluid into air that is then absorbed with water/sulphuric acid to form ammonium sulphate.
''This is termed air stripping and absorption. ''Finally, reverse osmosis is used to take out the potassium and produce a very clean water. ''As most minerals and synthetic compounds are removed in this process, the water may even be more pure than that we drink.
''However, we do not recommend the water from this process for human consumption, but it may be suited for cow consumption or to put back into the environment [fodder crop irrigation].''
Anaerobic digestion converted a fraction of the carbon into methane gas that could then be used for renewable energy and also ''conditions the by-product - digestate - for more simplistic solid liquid separation''.
''Most of the phosphorus and organic nitrogen [from the effluent] stays in the solids and the ammonia-nitrogen partitions into the liquid. ''The dry residual can also be used for animal bedding and other beneficial purposes.''
Anaerobic digestion had the advantages of being inexpensive, having low energy requirements and producing a renewable energy, Prof Safferman said.
Working with the university, McLanahan Corp had developed the nutrient separation system (NSS), which was expected to be available commercially by the end of the year.
The initial marketing of the NSS was directed at the dairy sector, but the technology was also applicable to other sectors of animal agriculture such as the pig industry. The system would be suitable for the average Otago-Southland dairy farm, Prof Safferman said.
''The process can minimise large storage requirements, as the separated components occupied a small fraction of the [volume] of the original manure ... [and] the water is used immediately for the cows, irrigated or surface-discharged. ''The farmer would need a digester and a processing facility to house the ultra-filtration, air-stripper and reverse osmosis processes. ''Pipes, mechanical equipment and storage tanks were also needed. ''The facility will resemble a wastewater treatment operation. ''Economies of scale applies, making this more suitable for a medium-sized farm - 500-plus cows.''
The final step of the process, reverse osmosis, was only required if a farmer wanted to generate very clean water, he said.
The system, in its current state of development, captured about 50% of the starting volume of manure as clean water.