Augmenting the Applicability and Efficiency of Ecological Engineering Solutions for Water Quality Improvement

The design options available to the ecological engineer were expanded by exploring new sustainable water quality improvement techniques, specifically the applicability of passive treatment of acid mine drainage (AMD) in high-altitude, arid environments, passive co-treatment of AMD and municipal wastewater (MWW), and ecologically engineered floating vegetation mats (EFVM).Field studies at Cerro Rico de Potosí, Bolivia demonstrated that AMD must be addressed to render local waters safe for agricultural use. AMD discharges from both operating and abandoned portals as well as tailings-related deposits displayed a high degree of heterogeneity with total metal concentrations ranging from 0.11-7,48l, <0.022-889, <0.0006-65.3, <0.001-310, 0.12-72,100, 0.3-402, <0.012-34.8, and 0.24-19,600 mg/L of Al, As, Cd, Cu, Fe, Mn, Pb and Zn, respectively. Net acidity and pH ranged from -10 to 246,000 mg/L as CaCO3 equivalent and 0.90-6.94 standard units, respectively. In-stream waters contained total metals concentrations of up to 16 mg/L As, 4.9 mg/L Cd, 0.97 mg/L Co, 1100 mg/L Fe, 110 mg/L Mn, 4.1 mg/L Pb, and 1500 mg/L Zn with pH ranging from 2.8-9.5. AMD-impacted streams contained elevated concentrations of the same major ecotoxic constituents present in AMD discharges at concentrations statistically greater than in those stream unimpacted by AMD. The data indicate that historic and current mining activities have transformed these key natural resources into potential human and environmental health hazards.To assess the viability of passive water quality improvement approaches for treating AMD from Cerro Rico, alkalinity production, acidity neutralization and metals removal were tracked for incubations of AMD in the presence of limestone (LS), a 1:1 mix of AMD and raw MWW, and a 1:1 mix of AMD and WW in the presence of LS. Three AMD sources from abandoned adits on Cerro Rico, raw WW from the city of Potosí and locally available LS were incubated in-situ for 72 hr in 1-L cubitainers. Although locally sourced LS can increase final alkalinity up to 397 mg/L as CaCO3, it is a prospective source for Mn and a few other potentially undesirable elements. Relevant to the prospects of AMD and WW passive co-treatment, mixing AMD with WW had relatively little effect on the final alkalinity achieved by LS dissolution. Accounting for dilution, dissolved concentrations of Ag, Al, As, Cd, Cr, Fe, Pb, Sb, Se, Sn, V and Zn decreased with AMD and WW incubation.In laboratory studies, passive co-treatment of AMD and MWW was further explored, resulting in a system that efficiently removed key constituents of both effluents. A laboratory-scale, four-stage continuous-flow reactor system was constructed to test the viability of simulated Cerro Rico high-strength AMD and MWW passive co-treatment. The synthetic AMD had pH 2.6 and 1860 mg/L acidity as CaCO3 equivalent and with 46, 0.25, 2, 290, 55, 1.2 and 390 mg/L of Al, As, Cd, Fe, Mn, Pb and Zn, respectively. The AMD was mixed at a 1:2 ratio with raw MWW from the City of Norman, Oklahoma containing 265 ± 94 mg/L BOD5, 11.5 ± 5.3 mg/L PO4-3, and 20.8 ± 1.8 mg/L NH4+-N and introduced to the system which had a total residence time of 6.6 d. During the 135 d experiment, dissolved Al, As, Cd, Fe, Mn, Pb and Zn concentrations were consistently decreased by 99.8, 87.8, 97.7, 99.8, 13.9, 87.9 and 73.4%, respectively, pH increased to 6.8 ± 0.1, and net acidic influent was converted to net alkaline effluent. PO4-3 and NH4+-N were decreased to <0.75 and 7.4 ± 1.8 mg/L, respectively. BOD5 was generally decreased to below detection limits. Nitrification increased NO3- to 4.9 ± 3.5 mg/L NO3--N, however relatively little denitrification occurred. Sulfate reducing bacteria were able to maintain a relatively high level of sulfate reduction (0.56 mol/m3-d). A 100% reduction of all fecal indicator bacteria was observed. Results indicated that passive AMD and MWW co-treatment is a viable ecological engineering approach for the developed and developing world that can be optimized and applied to improve water quality with minimal use of fossil fuels and refined materials.Field studies of EFVM illustrated that these systems could encourage water quality and temperature changes conducive to the passive treatment of various constituents. Four EFVM designs were constructed of drainpipe, burlap, mulch, utility netting, and reused polyethylene bottles then planted with Typha spp. and Juncus effusus. The water column beneath the EFVM in two test ponds was compared to that in an open water control pond. Dissolved oxygen concentrations and pH were lower, diurnal temperature range was dampened, and sulfate/nitrate reduction was greater under the EFVM with respect to the control. Alkalinity was also greater under EFVM. Although plant propagation was limited, results suggest that EFVM may be applied to encourage reducing, thermally insulated conditions for passive treatment of AMD and a wide range of other pollutants. Specifically, they may be employed to improve immediate and long-term performance of vertical flow bioreactors for AMD treatment by lowering dissolved oxygen concentrations in the water column and providing a continual source of organic carbon to the underlying substrate

Preliminary Assessment of Ferrate Treatment of Metals in Acid Mine Drainage

We report a preliminary assessment of ferrate [Fe(VI)] for the treatment of acid mine drainage (AMD), focused on precipitation of metals (i.e., iron [Fe] and manganese [Mn]) and subsequent removal. Two dosing approaches were studied to simulate the two commercially viable forms of Fe(VI) production: Fe(VI) only, and Fe(VI) with sodium hydroxide (NaOH). Subsequent metal speciation was assessed via filter fractionation. When only Fe(VI) was added, the pH remained99% when only NaOH was added, indicating that oxidation by Fe(VI) did not play a significant role when added. The Fe(III) and Al(III) particles were relatively large, suggesting probable success in subsequent removal through sedimentation. Resultant Mn-oxide particles were relatively small, indicating that additional particle destabilization may be required to meet Mn effluent goals. Ferrate seems viable for the treatment of AMD, especially when sourced through onsite generation due to the coexistence of NaOH in the product stream. More research on the use of Fe(VI) for AMD treatment is required to answer extant questions

Abatement of circumneutral mine drainage by Co-treatment with secondary municipal wastewater

Acid mine drainage is a persistent and problematic source of water pollution. Co-treatment with municipal wastewater at existing wastewater treatment plants has several advantages; however, potential impacts on plant physicochemical and biological processes have not been well explored. The primary purpose of this bench-scale study was to examine the impact of co-treatment by combining a mild acid mine drainage at various ratios with municipal wastewater, followed by sludge settling and supernatant comparative analysis using a variety of effluent water quality parameters. These measurements were combined with carbonate system and adsorption isotherm modeling to elucidate the mechanisms underlying the experimental results. Acid mine drainage addition decreased municipal wastewater effluent PO43− concentrations below 0.2 mg/L with greater than 97% removal, demonstrating co-treatment as an alternative solution for municipal wastewater nutrient removal. Biochemical oxygen demand remained similar to controls with \u3c10% variation after co-treatment. Coagulation from metals in acid mine drainage was incomplete due to PO43− adsorption, confirmed by comparing experimental results with Langmuir isotherm behavior. Sweep flocculation was the dominating particle aggregation mechanism, and co-treatment led to improved particle clarification outcomes. Improved clarification led to up to 50% Fe removal. Final pH had little variation with all conditions having pH \u3e 6.0. Carbonate system modeling adequately explains pH effects, and can also be applied to varying acid mine drainage matrices. The impact of acid mine drainage addition on the municipal wastewater microbial community was also investigated which provided evidence of microbial adaptation. This study demonstrates post-aeration co-treatment enables mitigation of mild acid mine drainage without adversely affecting wastewater treatment plant processes. Reported results also frame required future studies to address extant questions prior to full-scale adaptation

Potential Implications of Acid Mine Drainage and Wastewater Cotreatment on Solids Handling: A Review

Acid mine drainage (AMD) is a persistent and extensive source of water pollution and ecological degradation. Cotreating munici- pal wastewater (MWW) with AMD using existing infrastructure at conventional wastewater treatment plants (WWTPs) may serve as a potential option for AMD abatement. However, commonly elevated iron and aluminum concentrations and low pH of AMD could negatively impact various processes at a WWTP. The focus of this mini review was on determining how cotreating MWW with AMD could impact the solids handling processes at a WWTP. While no studies have explored the solids that could be generated during cotreatment in a WWTP, numerous articles separately discuss the solids generated during AMD or MWW treatment. Reviewing this literature revealed that iron and aluminum, common metals in AMD, are already present in MWW sludge and typically benefit most solids handling processes. The addition of AMD would elevate iron and aluminum concentration but would likely result in improved sludge dewatering, removal of odor-causing compounds during processing, and a decreased bioavailability of trace metals and water-soluble P in land applications. This review concludes that cotreating MWW with moderate to low volumes (\u3c50%) of AMD at WWTPs will have minimal impact on, and likely improve, solids handling processes

ANALYSIS OF MUNICIPAL WASTEWATER AND ACID MINE DRAINAGE PASSIVE CO-TREATMENT AT CERRO RICO DE POTOSÍ, BOLIVIA

Acid mine drainage (AMD) is a worldwide environmental problem. The passive co-treatment of AMD with municipal waste water (MWW) is a cost effective approach that uses nutrients in MWW in order to treat high concentrations of metals and sulfate found in AMD. Cerro Rico de Potosí in Bolivia is one of the biggest mining cities in the world, and it is constantly facing problems with AMD. The goal of this study was to determine the reaction rates of Al, Fe, Mn, Zn, and other metals found in an AMD discharge from Cerro Rico by a three-stage reactor system. The AMD had a pH of 3.58 and acidity of 1080 mg/L as CaCO3 equivalent containing 12, 68, 17 and 550 mg/L of dissolved Al, Fe, Mn, and Zn respectively. The reaction rates of Al, Fe, Mn, and Zn were 1.43, 2.09, 0.01, and 0.10 d-1, respectively

Assessment of sulphate and iron reduction rates during reactor start-up for passive anaerobic co-treatment of acid mine drainage and sewage

The fitted model parameters used to describe the behaviour of Fe, H₂S and SO₄<sup>2-</sup

Assessment of sulphate and iron reduction rates during reactor start-up for passive anaerobic co-treatment of acid mine drainage and sewage

The fitted model parameters used to describe the behaviour of Fe, H₂S and SO₄<sup>2-</sup