The addition of calcium carbonate to catchments or watercourses – liming – has been used widely to mitigate freshwater acidification but the abatement of acidifying emissions has led to questions about its effectiveness and necessity. We conducted a systematic review and meta-analysis of the impact of liming streams and rivers on two key groups of river organisms: fish and invertebrates. On average, liming increased the abundance and richness of acid-sensitive invertebrates and increased overall fish abundance, but benefits were variable and not guaranteed in all rivers. Where B-A-C-I designs (before-after-control-impact) were used to reduce bias, there was evidence that liming decreased overall invertebrate abundance. This systematic review indicates that liming has the potential to mitigate the symptoms of acidification in some instances, but effects are mixed. Future studies should use robust designs to isolate recovery due to liming from decreasing acid deposition, and assess factors affecting liming outcomes.

Further steps are needed to establish feasible alleviation strategies that are able to reduce the impacts of ocean acidification, whilst ensuring minimal biological side-effects in the process. Whilst there is a growing body of literature on the biological impacts of many other carbon dioxide reduction techniques, seemingly little is known about enhanced alkalinity. For this reason, we investigated the potential physiological impacts of using chemical sequestration as an alleviation strategy. In a controlled experiment, Carcinus maenas were acutely exposed to concentrations of Ca(OH)2 that would be required to reverse the decline in ocean surface pH and return it to pre-industrial levels. Acute exposure significantly affected all individuals’ acid–base balance resulting in slight respiratory alkalosis and hyperkalemia, which was strongest in mature females. Although the trigger for both of these responses is currently unclear, this study has shown that alkalinity addition does alter acid–base balance in this comparatively robust crustacean species.

The subalpine and alpine areas in North-Western Italy and Southern Switzerland (Canton Ticino) receive high deposition of atmospheric pollutants transported from emission sources in the Po Valley. Long-term studies on high-altitude lakes in these areas indicate widespread recovery from acidification, even though most of them are still substantially affected, especially by deposition of nitrogen compounds. We analysed long-term trends of the major chemical compounds in a sample (n = 41) of high-altitude lakes, both at the site and regional levels, with the aim to assess the response of water chemistry to changes in atmospheric deposition and climate. These lakes have been studied since the early 1980s in the context of research programmes on acidification and atmospheric pollution. The significant decrease of sulfate and acidity in atmospheric deposition led to acidification recovery in the majority of the lakes. However, some lakes are still acidic or show a high sensitivity to acidification. This sensitivity is particularly evident at the snowmelt, when alkalinity is still fully depleted in some lakes. At present, nitrate is the dominant acidifying agent in the studied lakes, due to the high input of nitrogen compounds from atmospheric deposition. Our study also demonstrated that climatic factors interact with atmospheric deposition affecting the long-term changes in lake water.

The successive alkalinity-producing passive system (SAPPS) located in Gangneung, South Korea was designed to treat acid mine drainage. The performance of SAPPS has been monitored intensively for 3 years at the component level (influent, settling pond A, the successive alkalinity-producing system (SAPS), settling pond B, constructed wetland, and effluent). This study evaluated the ability of SAPPS to remove acidity and iron from influents at flow rates ranging from 17 to 160 m3/day. The concentration of soluble Fe total was the highest, and the pH was the lowest at low flow rates (≤61 m3/day). When flow rates were over 80 m3/day, concentrations decreased and Fetotal was removed primarily at the SAPS stage. For flow rates of less than 61 m3/day, Fetotal was removed at the SAPS stage as well as in settling pond B and at the constructed wetland. Hydraulic retention times of 1 and 2 days were found to be appropriate and economical for use with the SAPS stage and for settling pond B and the constructed wetland, respectively The treatment of acid mine drainage by conventional SAPPSs is limited by the availability of alkaline materials. However, the new proposed system can address this weakness through the provisioning of a suitable alkalinity supply. © 2013 Springer Science+Business Media Dordrecht.

Synthetic wastewaters are widely used in many fields of wastewater research and operational management. However, few comparative studies have been conducted on the large number of published formulations. Eleven synthetic formulations simulating municipal wastewaters were selected based on their frequency of use, relative complexity, ease of formulation and cost and compared to two real municipal wastewaters. Synthetic wastewaters vary significantly in their compositions and characteristics, especially in terms of alkalinity, BOD K ₁, SOUR, BODU, COD/BOD and C/N/P ratio, although they are portrayed as ‘typical’ in terms of characteristics and suitability for use. The pH, alkalinity and the presence of Ca and Mg should be considered in combination with the diluent used. Where the diluent is tap water, then the presence of treatment chemicals should also be considered. The effects of the micronutrients present are also an important factor. The study found that no single formulation is appropriate for all situations. Both the Syntho and Synthes formulations attempt to simulate real wastewater, whereas other formulations primarily act as readily biodegradable vectors for toxicity analyses, characterisation studies and treatment process evaluations. The criteria for choosing a particular synthetic wastewater very much depend on its intended application and require careful selection.

Following the technical closure of the brown lignite Meirama mine (NW Spain) in April 2008, the reclamation of the mined area is being accomplished with the controlled flooding of its large pit. During the first 7 months of flooding, the sequential arrest of the ground water dewatering system led to the growth of an acidic water body of about 2 hm(3). Since October 2008, the surface waters from some local streams have been diverted towards the pit so that these have become the major water input in the flooding process. Surface water has promoted a major change in the chemical composition of the lake water so that, at present, its surface has a circum neutral pH, net alkalinity, and low conductivity. At present, the lake has slightly more than one half of its final volume, and it is expected the overflow in 3 to 3.5 years. The lake is meromictic, with a sharp chemocline separating the acidic monimolimnion (pH ≈ 3.2, acidity ≈ 150 mg CaCO3/L, κ 25 ≈ 2.4 mS/cm) from the main water body (pH ≈ 6.5, alkalinity ≈ 15 mg CaCO3/L, κ 25 ≈ 0.3 mS/cm). Oxygen is being depleted at the bottom of the lake so that the monimolimnion became anoxic in January 2011. Above the chemocline, the composition of the lake is similar, but not identical, to that of the flooding stream waters. Close to the surface, some constituents (pH, metals) show strong seasonal variations in coincidence with the phytoplankton growing periods. Those parameters whose limits are legally prescribed comply with the corresponding water quality standards, and they are also consistent with the forecasting results obtained in early modeling. At present, a project considering the construction of an uptake tunnel to exploit the lake is being developed for the emergency water supply of the metropolitan area of A Coruña.

Cryogenic time-resolved laser-induced fluorescence spectroscopy was successfully used to identify uranium binding forms in selected German mineral waters of extremely low uranium concentrations (<2.0 μg/L). The measurements were performed at a low temperature of 153 K. The spectroscopic data showed a prevalence of aquatic species Ca2UO2(CO3)3 in all investigated waters, while other uranyl-carbonate complexes, viz, UO2CO3(aq) and UO2(CO3)2 (2-), only existed as minor species. The pH value, alkalinity (CO3 (2-)), and the main water inorganic constituents, specifically the Ca(2+) concentration, showed a clear influence on uranium speciation. Speciation modeling was performed using the most recent thermodynamic data for aqueous complexes of uranium. The modeling results for the main uranium binding form in the investigated waters indicated a good agreement with the spectroscopy measurements.

Co-treatment of acid mine drainage (AMD) with municipal wastewater (MWW) using the activated sludge process is a novel treatment technology offering potential savings over alternative systems in materials, proprietary chemicals and energy inputs. The impacts of AMD on laboratory-scale activated sludge units (plug-flow and sequencing batch reactors) treating synthetic MWW were investigated. Synthetic AMD containing Al, Cu, Fe, Mn, Pb, Zn and SO4 at a range of concentrations and pH values was formulated to simulate three possible co-treatment processes, i.e., (1) adding raw AMD to the activated sludge aeration tank, (2) pre-treating AMD prior to adding to the aeration tank by mixing with digested sludge and (3) pre-treating AMD by mixing with screened MWW. Continuous AMD loading to the activated sludge reactors during co-treatment did not cause a significant decrease in chemical oxygen demand (COD), 5-day biochemical oxygen demand, or total organic carbon removal; average COD removal rates ranged from 87-93 %. Enhanced phosphate removal was observed in reactors loaded with Fe- and Al-rich AMD, with final effluent TP concentrations <2 mg/L. Removal rates for dissolved Al, Cu, Fe and Pb were 52-84 %, 47-61 %, 74-86 % and 100 %, respectively, in both systems. Manganese and Zn removal were strongly linked to acidity; removal from net-acidic AMD was <10 % for both metals, whereas removal from circum-neutral AMD averaged 93-95 % for Mn and 58-90 % for Zn. Pre-mixing with screened MWW was the best process option in terms of AMD neutralization and metal removal. However, significant MWW alkalinity was consumed, suggesting an alkali supplement may be necessary.