The drainage of contaminated mines could be treated with active and passive technologies (Hedin, 2013; Landers, 2011). It is considered that active treatment generally involves chemicals, machinery, and personnel associated with operations and sludge management (Anderson, 2013; Biehl & Inman, 2010; Burris, 2001). Passive treatment uses gravity, materials, and natural processes, under work and the production of marketable sludge (Hedin, 2013). Compared to passive systems, chemical processing systems have a smaller footprint and a smaller footprint. However, if the calculated duration is between 20 and 40 years, the cost of chemical treatment is generally 2 to 10 times greater than that of passive solutions. It is often argued that chemical treatment is more reliable than passive treatment (Van & Zee, 2015). A system presented was designed by Hedin Environmental (HE); a small consultancy specialized in the passive water treatment of the mine. Since 1994, HE has developed 47 passive processing systems, most of which are in Pennsylvania. The design of the system is in accordance with the Information Bulletin of the US Bureau of Mines. The design and performance data of existing systems and provides a decision tree for the design of passive systems (Xinchao & Shicheng, 2017). Other decision trees, including other technologies, have been developed. The tree contains technology independent of the supplier and HE has determined that it can reliably produce an effluent from the final system with a neutral pH and low metal concentrations (Hedin, 2013).
The ponds must conserve enough water to reach the objective of oxidation or deposition of solids. Water containing iron or dissolved organic material must be oxidized (Xinchao & Shicheng, 2017; Van & Zee, 2015; Burris, 2001). Water containing suspended solids of iron and aluminium hydroxide should settle. The size of the pond depends on the residence time or the metal load (Robert, et al., 2018). The basin is an important tool for the treatment of alkaline water contaminated with Fe, the drainage of the vertical flow basins and the drainage of the dry limestone bed (Robert, et al., 2018). The constructed wetland must be polished before draining (Anderson, 2013). The wetlands included here are aerobic and contain shallow water. Wetlands are generally positioned after the sedimentation basin to remove suspended solids that are difficult to remove in the basin. Wetlands are also used to eliminate manganese. Anoxic limestone runoff (ALD) is a layer of buried limestone that imparts alkalinity to the acidic water that flows during the dissolution of the carbonate. The name “drainage” is an ancient artefact system and is designed to resemble a French channel (Burris, 2001). A better term is an anoxic limestone bed. ALD is not suitable for water containing Al or Fe (III) (Fe3 +), since these metals form solids in the aggregates of limestone, which reduces their permeability and eventually clogs the system. As for water containing iron or manganese depleted in oxygen, ALD is the most effective and least expensive to treat acids (Anderson, 2013).
The aerobic limestone bed (OLB) is open to the atmosphere. The acid is neutralized by dissolving the carbonate. OLB was originally developed for pH adjustment and elimination of Mn (Robert, et al., 2018). The Mn is formed by the formation of a dense solid of Mn and, in most cases, the blockage of the aggregates does not occur for at least ten years. The elimination of manganese in aerobic limestone beds seems to be faster than in wetlands (Anderson, 2013). A new modification is the implementation of a limestone bed (DLB) in which the aerobic limestone bed (weekly) is evacuated periodically to maintain porosity and general permeability. It has been found that this method is used in the treatment of AMD, which contains Al and iron (III) without exposure to these metals during the problems of obstruction that occur during anoxic limestone (Anderson, 2013; Biehl & Inman, 2010).
The vertical flow cell (VFP) is a pond containing a layer of limestone aggregates covered with an alkaline organic matrix covered with water (Hedin, 2013; Robert & Robert, 2014; Robert, et al., 2018). The AMD is produced on the surface and passes through the vertical downward flow of Al to the organic substrate, in which the pH of the alkaline limestone thus generated is transmitted up and down (Xinchao & Shicheng, 2017). The lower drainage collects the water and releases it. VFP has been developed for acid waters containing aluminium and iron (III). Although these metals form a solid, the final contaminated substrate provides a large area provided by the vertical flow process and the substrate has a frontal inversion. Due to organic matter, the VFP effluent generally contains dissolved organic matter and reduced sulphur compounds. A sedimentation tank is needed to eliminate these contaminants (Robert & Robert, 2014).
The water treatment of the mine with a higher iron content (Fe 2+) requires the oxidation of Fe 2+. Fe3 and precipitate iron ox hydroxide solids. In passive systems, oxidation is generally considered a limiting step (Burris, 2001). The oxidation kinetics is strongly influenced by temperature. In climatic regions where the temperature varies greatly, Arrhenius-based calculations show that the oxidation kinetics is multiplied by ten during the hot and cold seasons. This kinetic damage will make any passive transformation impossible in the temperate climate of the northern latitude, subject to strict sewer restrictions. In fact, these strong seasonal fluctuations are often not observed. Many passive treatment systems have been built in the northern latitudes and are efficient throughout the year (Robert, et al., 2018). One of the most studied systems is the passive Marchand system in Pennsylvania (USA), where a large amount of Fe contamination is evacuated in depth during the entire treatment <3 mg / L of treated Fe (Burris, 2001). This review describes the processing performance of the Marchand system over the last six years and shows an unexpected chemical correlation with temperature that neutralizes the adverse effects of kinetics (Anderson, 2013).
With the historical progress of high-speed reactor, the ACP processes are considered the configurations to decouple SRT from HRT. In addition, it is considered that the biomass concentration of reactors is augmented using a secondary clarifier that has a reflux similar to its aerobic counterpart (Van & Zee, 2015). According to reports, the first ACP program was used to treat waste from diluted containers with a COD. The different versions of these high performance PCR systems from the first generation of medium effluents have failed. In practice, the main difficulty lies in the deficient segregation of the sludge from the water treated in the secondary clarifier (Anderson, 2013). Furthermore, it is considered that formation and biogas deposit in the sedimentation tank are other major problems. Furthermore, it is considered that the segregation of the sludge is attributed to a very intense excitement in the bioreactors, which results in small mud particle with little sedimentation (Biehl & Inman, 2010). Moreover, the supersaturating of dissolved gas causes the buoyancy in the clarifiers. Moreover, it is considered that the notion of intense mixture is to guarantee optimal interaction among the mud and the water (Hedin, 2013). Moreover, it is considered that modern systems operate in softer ACP mixing conditions while degassing units are usually equipped before secondary clarification. In fact, modern ACP systems for concentrated wastewater with relatively high SS concentrations are very effective. As a result, the ACP countries have a total market share in the range of high-speed systems (Robert & Robert, 2014). However, effluents from ACP countries require additional processing steps to comply with sewer restrictions. Another type of sludge retention has been discovered by introducing into a bioreactor an inert carrier material to which an organism can adhere (Landers, 2011). AF, also known as the fixed-bed method, has been developed as a carrier material for the biofilm system and joins the biofilm containing sludge particles between the voids contained in the biomass (adhesion of packaging material, and based on precipitation and formation of very good mud aggregates AF technology can be used in up and down flow reactors.
The AF system can be activated quickly by the application of suitable carrier materials, since the organisms effectively adhere to the inert carrier. The simple purification of the FA is the major reasons for their popularities in the 80s or 90s. In prolonged operations, problems usually occur with the AF system (Van & Zee, 2015). The main drawback of the AF concept is that it is difficult to uphold the desired interaction among the sludge and the effluent as it tends to clog the “bed.” This is especially true for partially soluble wastewater. These clogging problems can be solved at least partially by the use of a main decanter and / or cauterization step (Xinchao & Shicheng, 2017). However, this requires the constructions and operations of more unit. In addition to the high cost, the shortage problem (littering of the bed) will not be eliminated, which will result in ineffective treatments efficiency (Anderson, 2013). Furthermore, it is considered that AF technologies are massively utilized to treat wastewater from the beverages, foods, pharmaceuticals and chemical industry because of its high bio retention potential. Furthermore, it is considered that ascending flow devices 150-160 AF have been commissioned for the treatments of different type of wastewater, which represent approximately 6 percent of the complete installed high speed reactors. The experience of this system is, of course, quite satisfactory: it is suitable for relatively high load rates, up to 10 kg of COD m-3 day-1 (Burris, 2001).
Passive treatment is an option to treat contaminated runoff from abandoned mines. The design of an efficient passive treatment system requires an understanding of the chemical nature of the mine water and the capabilities of the state of the art (Biehl & Inman, 2010). Most of the mine drainage problems at the LAM sites in the Appalachian field can be resolved by simple passive techniques. This article presents a method for selecting techniques and provides examples of the long-term effects of four passive systems. Passive systems that are designed, built, and maintained properly offer extremely reliable processing at a much lower cost than an effective alternative (Burris, 2001).
The entrance to the system is a French drain previously installed for the collection of leaks from the mine. The flow control structure introduces a flow rate of up to 100 gallons per minute into a drainable calcareous bed that is introduced into the sedimentation basin. The dripping limestone bed is open to the atmosphere (Biehl & Inman, 2010).
It is considered that about 2 to 3% of all installed reactors are mixed reactors. For most applications, the majority of organic matter conversion occurs in the mud bed section, while the removal of a certain amount of contaminants in the filter section is at the top. For all compounds with a mixed system, the specific chemical effluent has a better treatment efficiency than the UASB reactor (Biehl & Inman, 2010). Robert, et al (2018) studied the biodegradation of complex phenolic mixtures in hybrid reactors, which combine the UASB and AF reactors. They found that the optimal ratio of COD / NO3-N for the maximum removal of COD and phenol was approximately 6.4. In this report, the COD and phenol removal rates were 96% and 99%, respectively (Hedin, 2013; Van & Zee, 2015; Burris, 2001). Their results show that phthalic acid can be converted to benzoate only at low concentrations of acetate and benzoate. Using a mixing system, the latter two become a mud bed zone, while the conversion of phthalic acid and other refractory compounds occurs in the mixed portion while maintaining a specific bacterial population (Anderson, 2013; Robert & Robert, 2014). Despite these laboratory results, the large plants used to treat PTA wastewater include only one-stage mud bed systems. Since these reactors are usually followed by a system for the subsequent treatment of activated sludge, the non-decomposed aromatic hydrocarbons are reacted aerobically (Xinchao & Shicheng, 2017).
The passive treatment system at the Marchand Mine is shown in Figure 2. 79o 45 ’55, 63W.
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