Remediation of acid mine drainage using microbial fuel cell based on sludge anaerobic fermentation

A review of passive acid mine drainage treatment by PRB and LPB: From design, testing, to construction

An extensive volume of acid mine drainage (AMD) generated throughout the mining process has been widely regarded as one of the most catastrophic environmental problems. Surface water and groundwater impacted by pollution exhibit extreme low pH values and elevated sulfate and metal/metalloid concentrations, posing a serious threat to the production efficiency of enterprises, domestic water safety, and the ecological health of the basin. Over the recent years, a plethora of techniques has been developed to address the issue of AMD, encompassing nanofiltration membranes, lime neutralization, and carrier-microencapsulation. Nonetheless, these approaches often come with substantial financial implications and exhibit restricted long-term sustainability. Among the array of choices, the permeable reactive barrier (PRB) system emerges as a noteworthy passive remediation method for AMD. Distinguished by its modest construction expenses and enduring stability, this approach proves particularly well-suited for addressing the environmental challenges posed by abandoned mines. This study undertook a comprehensive evaluation of the PRB systems utilized in the remediation of AMD. Furthermore, it introduced the concept of low permeability barrier, derived from the realm of site-contaminated groundwater management. The strategies pertaining to the selection of materials, the physicochemical aspects influencing long-term efficacy, the intricacies of design and construction, as well as the challenges and prospects inherent in barrier technology, are elaborated upon in this discourse.

Use of propionic acid additions to enhance zinc removal from mine drainage in short residence time, flow-through sulfate-reducing bioreactors

The effectiveness of liquid carbon additions to enhance zinc removal in laboratory-scale short hydraulic residence time (19 h) compost bioreactors receiving synthetic mine water with a high influent zinc concentration (45 mg/L) was investigated. Effective removal of such elevated zinc concentrations could not be sustained by sulfate reduction and/or other attenuation processes without carbon supplementation. Propionic acid addition resulted in improved and sustained performance by promoting the activities of sulfate reducing bacteria, leading to efficient zinc removal (mean 99%) via bacterial sulfate reduction. In contrast, cessation of propionic acid addition led to carbon limitation and the growth of sulfur oxidising bacteria, compromising zinc removal by bacterial sulfate reduction. These research findings demonstrate the potential for modest liquid carbon additions to compost-based passive treatment systems to engineer microbial responses which enhance rates of zinc attenuation in a short hydraulic residence time, enabling remediation of highly polluting mine drainage at sites with limited land availability.

Biodegradation of plastic monomer 2,6-dimethylphenol by Mycobacterium neoaurum B5-4

2,6-Dimethylphenol (2,6-DMP), an important chemical intermediate and the monomer of plastic polyphenylene oxide, is widely used in chemical and plastics industry. However, the pollution problem of 2,6-DMP residues is becoming increasingly serious, which is harmful to some aquatic animals. Microbial degradation provided an effective approach to eliminate DMPs in nature, which is considered as a prospective way to remediate DMPs-contaminated environments. But the 2,6-DMP-degrading bacteria is not available and the molecular mechanism of 2,6-DMP degradation is unclear as well. Here, a 2,6-DMP-degrading bacterium named B5-4 was isolated and identified as Mycobacterium neoaurum. M. neoaurum B5-4 could utilize 2,6-DMP as the sole carbon source for growth. Furthermore, M. neoaurum B5-4 could degrade 2,6-DMP with concentrations ranging from 1 to 500 mg L^-1. Six intermediate metabolites of 2,6-DMP were identified and a metabolic pathway of 2,6-DMP in M. neoaurum B5-4 was proposed, in which 2,6-DMP was initially converted to 2,6-dimethyl-hydroquinone and 2,6-dimethyl-3-hydroxy-hydroquinone by two consecutive hydroxylations at C-4 and γ position; 2,6-dimethyl-3-hydroxy-hydroquinone was then subjected to aromatic ring ortho-cleavage to produce 2,4-dimethyl-3-hydroxymuconic acid, which was further transformed to citraconate, and subsequently into TCA cycle. In addition, toxicity bioassay of 2,6-DMP in water using zebrafish indicates that 2,6-DMP is toxic to zebrafish and M. neoaurum B5-4 could effectively eliminate 2,6-DMP in water to protect zebrafish from 2,6-DMP-induced death. This work provides a potential strain for bioremediation of 2,6-DMP-contaminated environments and lays a foundation for elucidating the molecular mechanism and genetic determinants of 2,6-DMP degradation.

Toward Optimization of Wood Industry Wastewater Treatment in Microbial Fuel Cells—Mixed Wastewaters Approach

Microbial fuel cell (MFC) has the potential to become a promising sustainable technology of wastewater treatment. Usually, the investigations on MFCs are aimed at maximized power production in the system. In this article, we focused on the optimization of wood industry wastewater treatment in MFC, in combination with municipal wastewater as a source of microorganisms. We investigated the influence of different external resistance (2000 Ω, 1000 Ω, 500 Ω, and 100 Ω) on power density and wastewater treatment efficiency (chemical oxygen demand (COD) removal) in 1-month MFC operation time. We found that the highest COD removal was for MFCs under R = 1000 Ω after 22 days of MFC operation, while the highest current density was obtained for the lowest applied resistance. The results imply that wastewater treatment parameters such as resistance and time of MFC operation should be a subject of optimization for each specific type of wastewater used, in order to maximize either wastewater treatment efficiency or power production in MFC. Thus, optimization of power production and COD removal efficiency in MFCs need to be run separately as different resistances are required for maximizing these two parameters. When COD removal efficiency is a subject of optimization, there is no universal value of external resistance, but it should be set to the specific wastewater characteristics.

How to tackle the stringent sulfate removal requirements in mine water treatment-A review of potential methods

Sulfate (SO₄^2-) is a ubiquitous anion in natural waters. It is not considered toxic, but it may be detrimental to freshwater species at elevated concentrations. Mining activities are one significant source of anthropogenic sulfate into natural waters, mainly due to the exposure of sulfide mineral ores to weathering. There are several strategies for mitigating sulfate release, starting from preventing sulfate formation in the first place and ending at several end-of-pipe treatment options. Currently, the most widely used sulfate-removal process is precipitation as gypsum (CaSO₄·2H₂O). However, the lowest reachable concentration is theoretically 1500 mg L^-1 SO₄^2- due to gypsum's solubility. At the same time, several mines worldwide have significantly more stringent sulfate discharge limits. The purpose of this review is to examine the process options to reach low sulfate levels (< 1500 mg L^-1) in mine effluents. Examples of such processes include alternative chemical precipitation methods, membrane technology, biological treatment, ion exchange, and adsorption. In addition, aqueous chemistry and current effluent standards concerning sulfate together with concentrate treatment and sulfur recovery are discussed.

Improving bioelectricity generation and COD removal of sewage sludge in microbial desalination cell

Improving wastewater treatment process and water desalination are two important solutions for increasing the available supply of fresh water. Microbial desalination cells (MDCs) with common electrolytes display relatively low organic matter removal and high cost. In this study, sewage sludge was used as the substrate in the Microbial desalination cell (MDC) under three different initial salt concentrations (5, 20 and 35 g.L^-1) and the maximum salt removal rates of 50.6%, 64% and 69.6% were obtained under batch condition, respectively. The MDC also produced the maximum power density of 47.1 W m^-3 and the averaged chemical oxygen demand (COD) removal of 58.2 ± 0.89% when the initial COD was 6610 ± 83 mg L^-1. Employing treated sludge as catholyte enhanced COD removal and power density to 87.3% and 54.4 W m^-3, respectively, with counterbalancing pH variation in treated effluent. These promising results showed, for the first time, that the excess sewage sludge obtained from biological wastewater treatment plants could be successfully used as anolyte and catholyte in MDC, achieving organic matter biodegradation along with salt removal and energy production. In addition, using treated sludge as catholyte will improve the performance of MDC and introduce a more effective method for both sludge treatment and desalination.