Haal meer uit afvalwater
Utilizing treatment facilities to separate out organic matter for use as fertilizer on crops.
Current practices in the Netherlands means that Waste Water Treatment facilities take in a mixture of storm sewer water and household wastewaters. In most cases this water must run through several filters and lagoons, and then be exported or stored due to a mixture of heavy metals and pharmaceutical chemicals which makes the material harmful. The following proposal expands upon current practices to minimize these concerns to make the water viable for land reclamation or agricultural purposes while increasing the treatment facilities self-sufficiency. Unless otherwise noted, the steps are in addition to current treatment practices. First step- Ferric Hydroxide Filtration Unit for Heavy Metals As the waste water enters the treatment facility it will be run through a filter made of ferric hydroxide. An option for this filtration system is the Lennsorb 101 by LennTech. Adsorption through ferric hydroxide has been successfully used through many years for heavy metal removal in groundwater clean up as well as in treatment of process wastewaters. Lennsorb 101 adsorbs heavy metals such as chromium, uranium, copper and lead, as well as toxic elements including arsenic, antimony, vanadium, molybdenum and selenium. From their site, Lenntech states that “LENNSORB 101 can be used in adsorption filters, underground filtration beds and permeable reactive barriers around polluted soil. LENNSORB 101 adsorbs heavy metals such as chromium, uranium, copper and lead, as well as other toxic elements including arsenic, antimony, vanadium, molybdenum and selenium. Its adsorption capacity depends on the composition and properties of the water to be treated and the operating conditions.” Alternative First step- KDF Electro-Chemical Process KDF 55 and 85 are alternatives to the Lenntech filtration. Both systems use a Ferric Hydroxide granule for heavy metal and chemical removal. KDF mentions that a slight electrical charge is created, which could be used to power a small generator if the charge is enough. The generator could power or supplement the power required for moving the scrappers inside the tank or powering the aerators. Testing would need to take place to see if this charge is enough to do either of these items. KDF’s website gives the following information: “KDF 55 process medium is an effective chlorine removal agent used in point-of-entry (POE) treatment of municipal water supplies. KDF 85 process medium is an effective iron (ferrous) and hydrogen sulfide (H2S) removal agent that may be used alone or to protect existing water filtration/ purification technologies in POE treatment of groundwater supplies. These unique, innovative and environmentally responsible media consist of high purity copper-zinc granules that use redox (the exchange of electrons) in patented KDF® 55 and 85 Process Media in Point-of-Entry Water Treatment Systems – Chlorine, Iron and Hydrogen Sulfide Reduction products to effectively reduce/remove chlorine, iron, hydrogen sulfide, heavy metals, and control microorganisms in potable water without the use of chemicals. What’s more, KDF 55 and 85 media are highly efficient and tank size requirements are modest for more economical system engineering and installation.” *see word doc for table* Second step-Drying of Biosolids Drying of solid waste exiting the plant can now take place. With minimized heavy metal and chemical components, solids can be dried and used for agricultural or land mitigation efforts. An example product for use at this point is the Therma-Flite IC series biosolids dehydration system. According to their website, the biosolids dehydration system is designed to address the needs of the small to medium size municipality and to keep operator attention and maintenance cost to a minimum. The Therma-Flite IC Series BIO-SCRU® sludge dryer system is an automated continuous processor. All operating parameters are under the control of the PLC system and the automated process operates continuously, all with minimal operator attention. The BIO-SCRU® is effective in drying; digested, undigested primary, waste activated sludge and mixes of these types of sludge as is common for regional facilities. The system includes a feature to continuously remove buildup from the heat transfer surfaces and eliminates any large clumps from building and passing through the system via a series of cutters that break up the clumps and homogenize the particle size at each stage of the rotor. The BIO-SCRU® continuously produces 90%+ dry product with a variety of sludge consistencies due to three primary control factors. With the ability to control the feed rate into the dryer, the residence time in the dryer and the temperature of the dryer, the IC-Series BIO-SCRU® continually produces a dry product of consistent solids content. The heat energy for drying is indirect. Thermal fluid is circulated through the rotor, fluting and the outer jacket of the drying chamber in a closed loop path. The drying process operates under a slight negative pressure in a sealed chamber. Feed is extruded into the dryer from the feed hopper. A lock box and cooling screw maintain the seal at the discharge. An integrated scrubber/condenser removes the vaporized water from the system and captures any particulate. This dried solid matter can be collected by municipalities for land mitigation or sold off to agricultural companies for soil amendments. Third step-Constructed Wetlands for Biomass Harvesting and Filtration Upon exit of the facility, the remaining wastewater can be sent into man-made mitigated wetland lagoons for final cleaning and slow percolation into the groundwater. Constructed wetlands are engineered systems that use natural functions of the vegetation, soil, and organisms to treat wastewater. They are one example of phytoremediation. Similarly to natural wetlands, constructed wetlands also act as a biofilter and/or can remove pollutants such as heavy metals from the water. Some constructed wetlands may also serve as a habitat for native and migratory wildlife, although that is not their main purpose. There are two main types of constructed wetlands: subsurface flow and surface flow constructed wetlands. The planted vegetation plays an important role in contaminant removal. The filter bed, consisting usually of sand and gravel, has an equally important role to play, similar to what has been created in California at the Arcata Wastewater Treatment Plant and Wildlife Sanctuary. This facility is known as an innovative sewer management system employed by the city of Arcata, California. A series of oxidation ponds, treatment wetlands and enhancement marshes are used to filter sewage waste. The marshes also serve as a wildlife refuge, and are on the Pacific Flyway. It is at this final step that the primary agricultural matter can be harvested. Using fast-growing river cane native to the Netherlands, the treatment facility can trap any remaining heavy metal and chemical contaminants and grow a fast, carbon-neutral biofuel. It is considered carbon-neutral because the carbon that is trapped in the soil is typically rereleased when burned. IISD (Canada) carried out tests to assess the potential of cattail (Typha) as a biomass feedstock for biocarbon production. A comparison of cattail biocarbon was conducted against wheat straw biocarbon, evaluating energy content and various parameters from production. Cattail ash from solid fuel combustion trials in Blue Flame Stokers and cattail biochar was analyzed for agricultural nutrients nitrogen (N), phosphorus (P) and potassium (K). In addition, minor nutrients and heavy metal content were determined to ensure these concentrations would not limit land application. The tests conducted in this study indicate the majority of the total potassium would be available for plant usage at neutral soil pH. If cattail ash is washed with water to leach out soluble compounds, potassium is the only nutrient that is present in the filtrate, removing approximately 70 per cent of the soluble K and 30 per cent of the total K. Acidifying the ash has the effect of increasing the solubility of potassium so that total soluble K increases from 46 per cent to 81 per cent of TK when the pH is lowered to 6.7. Analysis for heavy metals and other nutrients concluded that no metals are present in cattail ash at a concentration that would prohibit its use as a fertilizer. Potential Biochar Cost-Savings for Waste Treatment Facilities Option 1 Research, yet to be completed, consists of experiments using biochar as an activated carbon medium to purify water and using cattail ash to raise liquid manure pH to remove phosphorus. Preliminary tests of cattail of biocarbon as an activated carbon have yielded excellent results, and it performs well as an activated carbon for water filtration. These tests may create an alternative activated carbon filter medium in the future that could cut costs on site at treatment facilities that harvest their own cattails. Option 2 The harvest of cattails from the wetlands and the subsequent creation of biofuel pellets can be a secondary market for the treatment facility or municipality. The biofuel could also be incorporated into the facilities energy plan if the faculties were changed or additional fuel sources were incorporated into the current infrastructure via a biogas generator. Addition of a generator could make the facility self-sufficient and more ‘green’. To realize this project a joint investment is needed by municipalities, agricultural and chemical companies, who will benefit from this investment in the long term.
MSc Organic Agriculture/Agroecology