Mop crops are used in effluent management to reduce runoff into waterways and other environmental systems. Agricultural or environmental crops, cultivated in “sewage farms”, are irrigated with sewage effluent as an alternative to discharging effluent into waterways.
Mop crops can be used to polish a range of wastewater types including domestic, agricultural or industrial wastewater. The wastewater provides valuable nutrients which are absorbed and converted into plant biomass. The rootzone is effective at removing pollutants, protecting groundwater. The plants can be harvested to produce economic products.
Mop crop plantations
Mop crop plantations can produce valuable environmental resources – such as ecological integrity and carbon sequestration; and economic resources – such as timber, fuel and food. For example, the Byron Bay effluent reuse wetland relies on 500,000 Melaleuca trees to achieve wetland regeneration, acid sulphate soil management and carbon sequestration. An effluent irrigation orchard at Jubullum Village produces citrus fruit for the community. The Bangalow Mop Crop Farm produces bamboo which is used for building materials and fuel. Ecoteam designs, constructs and operates mop crop plantations for a range of wastewater management systems.
Phytoremediation is a form of bioremediation which uses genetically engineered, specifically selected or naturally occurring plants to accumulate specific metals in plant biomass. Phytoremediation can be used to accumulate, immobilize and transform low level pollutants from soil and water. Phytoremediation can extract inorganic contaminants using ‘hyperaccumulators’, which are able to accumulate extremely high amounts of metals in their stems and leaves without being poisoned by toxicity. Inorganic contaminants can be remediated and removed by harvesting plant biomass or converted into a biologically inert form. Plants which can be harvested and incinerated and have the added benefit of reducing the volume and concentrations of contaminates and therefore reducing the costs of remediation. Low grade mineral ores are accumulated into plant biomass have to potential for extraction.
Aquatic plants such as water hyacinth,duckweed and pennywort are able to remove significant amounts of metals from water and mine tailings. Indian mustard can produce a high biomass and is successful in removing lead, chromium, copper, zinc, cadmium, selenium and nickel. The genus Alyssum contains over 50 species which have been able to achieve over 2.5% Nickel accumulation in dry leaf. Some hyperaccumulator species can maintain high levels of metal uptake even under saline conditions.
Soil-bourne fungi such as ectomycorrhizal fungi also form symbiotic associations with fine plant roots increasing nutrient availability and tolerance to high metal concentrations. The use of soil enhancers such as chelates can increase the availability of uptake of contaminants by roots. As well as the plants ability to ‘hyperaccumulate’ metals effectively phytoremediation also requires plants to be fast growing and have high biomass. Generally plants which are able to hyperaccumulate are also slow growing and have little biomass. Other methods of phytoremediation include phytostabilisation, which uses plant structure to stabilize contaminants reducing the bioavailability and mobility of the contaminants in the soil, preventing them from entering the food chain or groundwater.