ZVI=Zero Valent Iron (Fe0), correctly elemental iron. Elemental iron is very reactive; it oxidizes in air to give iron oxide, also known as rust. While iron itself oxidizes, the reaction-partner is reduced.
The application of elemental iron in environmental technologies is based on its reducing behaviour in water and soil. By the chemical reduction of soil- and groundwater contaminants, ZVI is able to change the chemical form and as a consequence the mobility (water solubility, biodegradability) of certain contanminants, e.g. the conversion of sulphates into sulfides or co-precipitate metals when changing them from ionic form to hydroxides or oxides. In other cases elemental iron it is able to catalyse chemical degradation of chlorinated componds, such as chlorinated solvents or pesticides by reductive dechlorination.
In environmental application the iron nanoparticles (NZVI) proved to be very efficient due to high specific surface area and easy transport in solid soil.
zero-discharge technology comprises industrial processes designed to prevent the release of any pollutant harmful to the environment (e.g. recovery of solvents, cleaning rinses, and other chemicals used in manufacturing by collecting them and removing dissolved and suspended materials so the liquids can be reused).
zero waste agriculture is a type of sustainable agriculture which optimizes use of the plants, animals, bacteria, fungi and algae, to produce biodiverse-food, energy and nutrients in a synergistic integrated cycle of profit making processes where the waste of each process becomes the feedstock for another process.
The biogas digester is the heart of most zero waste agriculture (ZWA) systems. It is a 3000 year old anaerobic digestion process, where all organic waste can be converted into biogas, which is used for heating. The residue of anaerobic digestion is utilised for algae production, and agae for growing fish. Microalgae can alternatively be utilised for biodiesel-production. In sunny climates, a one hectare zero waste farm can produce over 1000 litres of oil in a year from the chlorella microalgae grown on biogas digester effluent in a 500 squermeter shallow pond. The nutritive high protein waste from the oil extraction process can be used as animal feed.
The water recycling can also be made complete in such an agricultural system: all the used waters can be naturally treated and reused.
Zero waste agriculture combines ecological or organic farming practices with a complete waste utilisation system.
Zero waste agriculture is optimally practiced on small 1−5 ha sized family owned and managed farms and it complements traditional farming & animal husbandry as practiced in most third world communities. Zero Waste Agriculture also preserves local indigenous systems and existing agrarian cultural values and practices.
Zero waste agriculture presents a balance of economically, socially and ecologically benefits as it:
- optimizes food production in an ecological sound manner
- reduces water consumption through and recycling and reduced evaporation
- provides energy security through the harvesting of biomethane (biogas) and the extraction of biodiesel from micro-algae all of which from as a by-products of food production
- provides climate change relief through the substantial reduction in greenhouse gas emissions from both traditional agriculture practices and fossil fuel usage
- reduces the use of pesticides through biodiverse farming.
ZWA is a target of the agrarpolitics in many third countries, such as Brazil, India, China, Columbia and South Africa.
zoobenthos are the animal organisms which live on, in, or near the bed of any surface water: stream- and riverbeds, seabed, the sediment of lakes, tidal pools, foreshores, both in the surface of the bottom-sediment and the deeper layers. In the sea and in the oceans many organisms adapted to deep-water pressure cannot survive in the upper parts of the water column.
Because light does not penetrate surface waters and deep ocean-water, the energy source for benthic ecosystems is often organic matter from higher up in the water column which drifts down to the depths. The dead organic matter, the decaying matter is the nutrient source of the benthic ecosystem: many of the benthic animals are scavengers or detrivores.
Zoobenthos generally live in close relationship with the substrate bottom; many such organisms are permanently attached to the bottom. The superficial layer of the soil lining the given body of water, the benthic boundary layer, is an integral part of the benthic zone, as it influences greatly the biological activity which takes place there. Examples of contact soil layers include sand bottoms, rock outcrops, coral, and bay mud.
By location we distinguish between epibenthos, living on top of the sediment, and hyperbenthos, living just above the sediment.
According to the size of the organisms we differentiate between
- macrozoobenthos: larger, more visible, animals, greater than 0.5 mm in size, such as worms, crabs, clams, sediment-living fishes, insects;
- meiozoobenthos: tiny benthos that are less than 0.5 mm but greater than 32 µm in size, such as nematodes, foraminiferans, water bears, gastrotriches and smaller crustaceans such as copepods and ostracodes.
- microzoobenthos: microscopic benthos that are less than 32 µm in size. Some microanimals: ciliates, amoeba.