Technology Strengths, Weaknesses and Critical Indicators
Clean Water Membrane Systems can be used to reduce both suspended and dissolved solids depending on location specific requirements:
- Can produce recycled dischargeable water (RO) and marketable products when paired with other technologies
- Always produces two streams leaving system a stream retained and a stream that permeates the membrane.
- Membranes of various size are often used together to achieve cleaner water: microfiltration or ultrafiltration membranes first followed by reverse osmosis membranes—each allowing various sized particles through the membrane
- Reverse Osmosis membranes are required to remove salts and achieve water suitable for discharge
- Depending on the membrane, effective pre-treatment to remove coarse, fibrous solids as well as fine suspended solids are important to system viability and reliability
- Membrane failure and high pressure/energy costs can be a concern
- Proven technology for nitrogen recovery, phosphorous recovery, and storage reduction
- Dairies desiring significant reduction in liquid manure storage volume and added flexibility in land application options.
- Dairies under unique constraints related to storage capacity, lagoon construction/cost, and/or manure hauling to distant fields.
- The technology is available at any scale.
- Both raw and digested manure can be treated but significant pre-treatment of those manures is required.
- Technology is applicable to all climate conditions.
Economic/Return on Investment Considerations
- Capital costs are a concern with installed costs on the high end.
- Operating costs are high, with systems incurring high electrical and chemical costs.
- Significant offset of manure management costs. From 40-70% of pre-treated liquid volume can be converted to ‘clean water’ not requiring storage and application.
- Although markets are not mature, and several factors impact its viability, the concentrate resulting from the removal of water, can be sold for value.
- As of 2018, the number of U.S. installations is around one dozen, mostly at dairies of a smaller size.
- An analysis of locations shows the adoption of the technology to dairies with unique costs related to liquid storage/application.
- The state of the technology in the U.S. is emerging. Presently, significant concerns exist relating to operational uptime, reliability, and true operational costs.
- Multiple vendors and configurations exist, with systems using varying types, forms and sequences of membranes.
- Storage volume reduction, 40-70% of incoming liquid resulting in ‘clean water’ suitable for either discharge, use as process water or animal drinking water—pending meeting local and federal regulations.
- Nutrients partitioned into a concentrated liquid product.
- Produces a concentrate containing virtually all of the incoming nutrients/salts.
- Negligible impact on odor is seen with this technology.
- Produced concentrate can have bacteria/virus partitioned into smaller volumes, although the pathogens are not destroyed.
- GHG mitigation is negligible as the initial organics remain in the concentrated form.
- Offsets to existing manure management, specifically lagoon storage maintenance/construction and liquid transportation.
- ‘Clean water’ produced by system can potentially be used as process water, animal drinking water, and new water rights upon discharge to streams—all of which can produce limited offsets and/or revenues, with proper permitting.
- Produced concentrate could be certified organic, producing a value-added liquid fertilizer concentrate for the organic market.
How it works
- Pre-treated manure, with suspended solids removed, are passed through a sequence of membranes using high-pressure pumps. As the liquid enters the membranes, certain nutrients/salts/pathogens are rejected by the size of the membrane while water and other species pass through.
- The rejected material becomes the liquid concentrate while the pass-through becomes the ‘clean water’
- The end products of the process are the liquid concentrate containing the bulk of influent nutrients/salts and a ‘clean water’ with potential for discharge, use as process water, and/or animal drinking water, pending permitting.
Pretreatment and/or Post-treatment Required
- Effective pretreatment is essential. For protection of the membranes, manure must be removed of nearly all suspended solids.
- The liquid concentrate will require storage/application while the ‘clean water’ will need to meet permitting requirements for desired end-use. In the case of discharge to U.S. waterways, a particularly intensive permitting process, the post-treatment might require additional treatments such as ion exchange, activated carbon, oxygenation, outflow processing, etc.
- Key limitations of the technology center on both the high cost and on-going concerns with reliability.
- No renewable energy is produced in this system and considerable electrical energy is required.
- No thermal renewable energy is produced in the system.
- Successful projects require a correct matching of technology with specific volume reduction and corresponding reduction in transportation costs.
- Correct choice of system and operations/maintenance are required to overcome historic reliability and performance concerns.
- Creative use can decrease costs, such as operating the system only during the winter months of required storage or only treating a fraction of manure.
- Pretreatment with chemical coagulants or flocculants could impact organic certification. Review of products used should be conducted to determine potential effects on certification.
Skilled operations/maintenance, either internal with training or external with professional services, are required for sustained and reliable operation
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