Comparison of the efficiency of chitinous and ligneous substrates in metal and sulfate removal from mining-influenced water

High Efficacy Two-Stage Metal Treatment Incorporating Basic Oxygen Furnace Slag and Microbiological Sulfate Reduction

Lignocellulosic sulfate-reducing biochemical reactors (SRBRs) can be implemented as passive treatment for mining-influenced water (MIW) mitigating the potentially deleterious effects of MIW acidic pH, and high concentrations of metal(loid)s and SO42-. In this study, a novel two-stage treatment for MIW was designed, where basic oxygen furnace slag (slag stage) and microbial SO42- reduction (SRBR stage) were incorporated in series. The SRBRs contained spent brewing grains or sugarcane bagasse as sources of lignocellulose. The slag reactor removed >99% of the metal(loid) concentration present in the MIW (130 ± 40 mg L-1) and increased MIW pH from 2.6 ± 0.2 to 12 ± 0.3. The alkaline effluent pH of the slag reactor was mitigated by remixing slag effluent with acidic MIW before SRBR treatment. The SRBR stage removed the bulk of SO42- from MIW, additional metal(loid)s, and yielded a circumneutral effluent pH. Cadmium, copper, and zinc showed high removal rates in SRBRs (≥96%) and likely precipitated as sulfide minerals. The microbial communities developed in SRBRs were enriched in hydrolytic, fermentative, and sulfate-reducing taxa. However, the SRBRs developed distinct community compositions due to the different lignocellulose sources employed. Overall, this study underscores the potential of a two-stage treatment employing steel slag and SRBRs for full-scale implementation at mining sites.

Effective assessment of biopolymer-based multifunctional sorbents for the remediation of environmentally hazardous contaminants from aqueous solutions

Persistent contaminants in wastewater effluent pose a significant threat to aquatic life and are one of the most significant environmental concerns of our time. Although there are a variety of traditional methods available in wastewater treatment, including adsorption, coagulation, flocculation, ion exchange, membrane filtration, co-precipitation and solvent extraction, none of these have been found to be significantly cost-effective in removing toxic pollutants from the water environment. The upfront costs of these treatment methods are extremely high, and they require the use of harmful synthetic chemicals. For this reason, the development of new technologies for the treatment and recycling of wastewater is an absolute necessity. Our way of life can be made more sustainable by the synthesis of adsorbents based on biomass, making the process less harmful to the environment. Biopolymers offer a sustainable alternative to synthetic polymers, which are manufactured by joining monomer units through covalent bonding. This review presents a detailed classification of biopolymers such as pectin, alginate, chitosan, lignin, cellulose, chitin, carrageen, certain proteins, and other microbial biomass compounds and composites, with a focus on their sources, methods of synthesis, and prospective applications in wastewater treatment. A concise summary of the extensive body of knowledge on the fate of biopolymers after adsorption is also provided. Finally, consideration is given to open questions about future developments leading to environmentally friendly and economically beneficial applications of biopolymers.

Decreasing lactate input for cost-effective sulfidogenic metal removal in sulfate-rich effluents: Mechanistic insights from (bio)chemical kinetics to microbiome response

High material cost is the biggest barrier for the industrial use of low-molecular-weight organics (i.e. lactate) as external carbon and electron source for sulfidogenic metal removal in sulfate-rich effluents. This study aims to provide mechanistic evidence from kinetics to microbiome analysis by batch modeling to support the possibility of decreasing the lactate input to achieve cost-effective application. The results showed that gradient COD/SO42- ratios at a low level had promising treatment performance, reaching neutralized pH with nearly total elimination of COD (91%-99%), SO42- (85%-99%), metals (80%-99%) including Cu, Zn, and Mn. First-order kinetics exhibited the best fit (R2 = 0.81-0.98) to (bio)chemical reactions, and the simulation results revealed that higher COD/SO42- accelerated the reaction rate of SO42- and COD but not suitable to that of metals. On the other hand, we found that the decreasing COD/SO42- ratio increased average path distance but decreased clustering coefficient and heterogeneity in microbial interaction network. Genetic prediction found that the sulfate-reduction-related functions were significantly correlated with the reaction kinetics changed with COD/SO42- ratios. Our study, combining reaction kinetics with microbiome analysis, demonstrates that the use of lactate as a carbon source under low COD/SO42- ratios entails significant efficiency of metal removal in sulfate-rich effluent using SRB-based technology. However, further studies should be carried out, including parameter-driven optimization and life cycle assessments are necessary, for its practical application.

Dissolved organic matter composition and fluorescence characteristics of the river affected by coal mine drainage

Coal mine drainage (CMD) discharged into surface waters results in serious environmental pollution risk to rivers, lakes, and reservoirs. Coal mine drainage generally contains a variety of organic matter and heavy metals due to coal mining activities. Dissolved organic matter (DOM) plays an important role in the physicochemical and biological processes of many aquatic ecosystems. In this study, the investigations were carried out in the dry and wet seasons in 2021 to assess the characteristics of DOM compounds in coal mine drainage and the CMD-affected river. The results indicated that the pH of CMD-affected river pressed close to coal mine drainage. Besides, coal mine drainage lowered DO by 36% and increased total dissolved solids by 19% in the CMD-affected river. Coal mine drainage decreased absorption coefficient a(350) and absorption spectral slope S_275-295 of DOM in the CMD-affected river; hence, DOM molecular size increased with decreasing S_275-295. Three-dimensional fluorescence excitation-emission matrix spectroscopy and parallel factor analysis identified humic-like C1, tryptophan-like C2, and tyrosine-like C3 in the CMD-affected river and coal mine drainage. DOM in the CMD-affected river mainly originated from microbial and terrestrial sources, with strong endogenous characteristics. The ultra-high-resolution Fourier transform ion cyclotron resonance mass spectrometry analysis revealed that coal mine drainage had a higher relative abundance of CHO (44.79%), with a higher unsaturation degree of DOM. Coal mine drainage decreased the AI_mod,wa, DBE_wa (double bond equivalents), O_wa, N_wa, and S_wa values and increased the relative abundance of the O₃S₁ species with DBE of 3 and carbons number range of 15-17 at the CMD inlet to the river channel. Moreover, coal mine drainage with the higher protein content increased the protein content of water at the CMD inlet to the river channel and the downstream river. DOM compositions and proprieties in coal mine drainage were investigated to further understand the influence of organic matter on heavy metals in future study.

Continuous-mode acclimation and operation of lignocellulosic sulfate-reducing bioreactors for enhanced metal immobilization from acidic mining-influenced water

Lignocellulosic sulfate-reducing bioreactors are an inexpensive passive approach for treatment of mining-influenced water (MIW). Typically, microbial community acclimation to MIW involves bioreactor batch-mode operation to initiate lignocellulose hydrolysis and fermentation and provide electron donors for sulfate-reducing bacteria. However, batch-mode operation could significantly prolong bioreactor start-up times (up to several months) and select for slow-growing microorganisms. In this study we assessed the feasibility of bioreactor continuous-mode acclimation to MIW (pH 2.5, 6.5 mM SO₄^2-, 18 metal(loid)s) as an alternate start-up method. Results showed that bioreactors with spent brewing grains and sugarcane bagasse achieved acclimation in continuous mode at hydraulic retention times (HRTs) of 7-12-d within 16-22 days. During continuous-mode acclimation, extensive SO₄^2- reduction (80 ± 20% -91 ± 3%) and > 98% metal(loid) removal was observed. Operation at a 3-d HRT further yielded a metal(loid) removal of 97.5 ± 1.3 -98.8 ± 0.9% until the end of operation. Sulfate-reducing microorganisms were detected closer to the influent in the spent brewing grains bioreactors, and closer to the effluent in the sugarcane bagasse bioreactors, giving insight as to where SO₄^2- reduction was occurring. Results strongly support that a careful selection of lignocellulose and bioreactor operating parameters can bypass typical batch-mode acclimation, shortening bioreactor start-up times and promoting effective MIW metal(loid) immobilization and treatment.

Chitin as a Sorbent Superior to Other Biopolymers: Features and Applications in Environmental Research, Energy Conversion, and Understanding Evolution of Animals

Chitin is an effective sorbent which can be used in environmental monitoring, beyond obvious applications in withholding metal-containing pollutants from wastewater- or nuclear fuel reprocessing flows, since background levels in (purified) chitin are very low except for a few metals (Fe, Cu, Al, Ti, and Zn). Since retention of Mx+ and their complexes on chitin depend on an oxidation state, and to a lesser extent the presence of possible ligands or co-ligands, partition between chitin samples exposed to sediment and those exposed to water can be changed by environmental factors such as local biota producing or absorbing/metabolizing effective ligands such as citrate or oxalate and by changes of redox potential. Thermodynamics are studied via log P, using calibration functions log P vs. 1/r or log P vs. Σσ (sum of Hammett parameters of ligand donor groups) for di- and trivalent elements not involved in biochemical activity (not even indirectly) and thus measuring “deviations” from expected values. These “deviations” can be due to input as a pollutant, biochemical use of certain elements, precipitation or (bio-induced reduction of SO42− or CO2) dissolution of solids in sediment. Biochemical processes which occur deep in sediment can be detected due to this effect. Data from grafted chitin (saturation within ≤ 10 min) and from outer surfaces of arthropods caught at the same site do agree well. Log P is more telling than total amounts retrieved. Future applications of these features of chitin are outlined.

Biostimulation of sulfate-reducing bacteria and metallic ions removal from coal mine-impacted water (MIW) using shrimp shell as treatment agent

This paper comprises several assays aiming to identify the basis for the bioremediation of mine-impacted water (MIW). To do so, the conditions for build anoxic microcosms for treating this effluent were varied, containing MIW, and a source of chitin, to biostimulate sulfate-reducing bacteria (SRB). The chitin sources were: commercial chitin (CHIT) and shrimp shell (SS), which in addition to chitin, contains CaCO₃, and proteins in its composition. The CHIT assays were not successful in sulfate-reduction, even when the pH was increased with CaCO₃. However, in all SS assays the SRB development was successful (85% sulfate removal for assay 3), including the metal-free (MF-SS) assay (75% for assay 5). High-throughput sequencing analysis revealed the structure of bacterial community in the SS assay: the most abundant genera were Clostridium and Klebsiella, both fermentative and chitinase producers; a few SRB from the genera Desulfovibrio and Desulfosporosinus were also detected. In the MF-SS assay, Desulfovibrio genuswas detected but Comamonas was dominant. It could be deduced that SS is a suitable substrate for SRB development, but CHIT is not. The sulfate-reduction process was provided by the cooperation between fermentative/chitinase-producer bacteria together with SRB, which leads to efficient MIW treatment, removing sulfate and metallic ions.

Source identification and component characterization of dissolved organic matter in an acid mine drainage reservoir

Acid mine drainage (AMD) is one of the most serious environmental problems and extreme environments on the earth, with high concentrations of sulphate and dissolved metals. A comprehensive description of dissolved organic matter (DOM) in these reservoirs is lacking, and it can play an important role in AMD pollution treatment and ecosystem. Thus, the source, composition and property of DOM in an AMD reservoir in Ma'an shan, China were studied using Fourier transform ion cyclotron resonance mass spectrometry and three-dimension excitation emission matrix fluorescence spectroscopy. The results suggested that the autochthonous algal metabolites significantly contributed to the DOM pool in the AMD reservoir. Bioavailable substances with lower oxidation, unsaturation and aromaticity such as lipids and carbohydrates were lacking in the AMD reservoir especially in the deeper layers. In addition, the proportion of sulfur compounds was significantly higher than that in other waters, suggesting the potential formation of organic matter with sulfur atom in a sulfur-rich environment. These findings underscore that the investigation of DOM in AMD reservoirs may offer references for the AMD treatment with addition of organic matter and broaden the understanding of special carbon cycling in the extreme environment of AMD.

Advances in heavy metal removal by sulfate-reducing bacteria

Industrial development has led to generation of large volumes of wastewater containing heavy metals, which need to be removed before the wastewater is released into the environment. Chemical and electrochemical methods are traditionally applied to treat this type of wastewater. These conventional methods have several shortcomings, such as secondary pollution and cost. Bioprocesses are gradually gaining popularity because of their high selectivities, low costs, and reduced environmental pollution. Removal of heavy metals by sulfate-reducing bacteria (SRB) is an economical and effective alternative to conventional methods. The limitations of and advances in SRB activity have not been comprehensively reviewed. In this paper, recent advances from laboratory studies in heavy metal removal by SRB were reported. Firstly, the mechanism of heavy metal removal by SRB is introduced. Then, the factors affecting microbial activity and metal removal efficiency are elucidated and discussed in detail. In addition, recent advances in selection of an electron donor, enhancement of SRB activity, and improvement of SRB tolerance to heavy metals are reviewed. Furthermore, key points for future studies of the SRB process are proposed.

A novel carbon monoxide fed moving bed biofilm reactor for sulfate rich wastewater treatment

In this study, a moving bed biofilm reactor was used for biodesulfuruization using CO as the sole carbon substrate. The effect of hydraulic retention time (HRT), sulfate loading rate and CO loading rate on sulfate and CO removal was examined. At 72, 48 and 24 h HRT, the sulfate removal was 93.5%, 91.9% and 80.1%, respectively. An increase in the sulfate loading reduced the sulfate reduction efficiency, which, however, was improved by increasing the CO flow rate into the MBBR. Best results in terms of sulfate reduction (>80%) were obtained for low inlet sulfate and high CO loading conditions. The CO utilization was very high at 85% throughout the study, except during the last phase of the continuous bioreactor operation it was around 70%. An artificial neural network based model was successfully developed and optimized to accurately predict the bioreactor performance in terms of both sulfate reduction and CO utilization. Overall, this study showed an excellent potential of the moving bed biofilm bioreactor for efficient sulfate reduction even under high loading conditions.

Mine drainage: Treatment technologies and rare earth elements

The recent research and development on mine drainage published in 2018 was summarized in this annual review. In particular, this review was focused on two main aspects of mine drainage: (a) advances in treatment technologies and (b) rare earth elements in mine drainage and its recovery. The first section covers passive treatment technologies and active treatment options, including physiochemical treatment and biological treatment. The second section includes the characterization of rare earth elements in mine drainage and recovery technologies. Due to the importance of rare earth elements and the growing interest in their recovery from mine drainage, rare earth elements are reported as a separate section for the first time in this review. PRACTITIONER POINTS: Advances in treatment technologies for mine drainage are reviewed. Rare earth elements in mine drainage and its recovery are summarized. Reviewed technologies include passive, active, advanced and novel processes.

Changes in microbial communities of a passive coal mine drainage bioremediation system

Drainage from abandoned mines is one factor greatly affecting the streams and vegetation in and around Pittsburgh and the Appalachian Mountains where coal mining occurred. This drainage may be more acidic, alkaline, or metal based. Different methods for remediation exist. Passive remediation is one method used to naturally allow the metals to precipitate out and aid in cleaning up the water. The goal of this study is to sample different holding ponds in a sequential passive remediation system and determine microbial communities present at each site of an abandoned coal mine drainage site. Sequencing of the 16S rRNA gene of the sediment indicated the most abundant phyla at each of the 5 ponds and wetland area included Proteobacteria (36%–43%), Bacteroidetes (12%–37%), Firmicutes (3%–11%), and Verrucomicrobia (6%–11%). Analysis of genera between the first, and most polluted, pond included Solitalea, Pedosphaera, and Rhodocyclus, whereas the microbial community from the wetland site at the end of the remediation system included Ignavibacterium, Pelotomaculum, and Petrimonas. The results of our microbial community composition study of sediment from a passive treatment system are in line with organisms commonly found in sediment regardless of iron oxide precipitation, while others are preferentially found in the less polluted wetland site.