Nitrification in Constructed Wetlands Treating Ochreous Mine Water

A survey of ochreous discharges from former coal mines in the UK indicated ammonia contamination at 2–5 mg/L in water from flooded shafts of depths >400–800 m. Although significant, this was much less than historically observed in working mines. No correlation was observed between ammonia and iron concentrations. However, ammonia was removed to some extent in constructed wetlands designed primarily to remove iron. A mechanistic study of wetland removal of ammonia from mine water indicated the main process to be bacterial nitrification, similar (despite great differences in operating conditions) to that occurring in many wastewater treatment works. The study was based on water containing 4–5 mg/L ammonia and some 12–27 mg/L iron from the abandoned Woolley mine in Yorkshire. Notwithstanding relatively high salinity and short residence time, most of the ammonia entering the wetlands was, at least initially, converted to nitrate. Field measurements showed that the conversion efficiency was increased at lower flow rates, higher temperature, and longer flow stabilisation, which are all consistent with bacterial action. Subsurface flow conditions were simulated in column studies, using pre-sterilised gravel and mine water taken from the wetland cells; two strains of bacteria commonly associated with nitrification in domestic wastewaters, Nitrosomonas europaea and Nitrobacter agilis, were able to reproduce the 89% ammonia oxidation observed in the wetlands. It was concluded that the high degree of aeration, neutral pH, and nutrient content of the mine water greatly favoured nitrification. Although more saline and lower in biochemical oxygen demand than organic wastewater, nitrification was not inhibited.     

Magnitude and timing of nictitating membrane movements during classical conditioning of the rabbit (Oryctolagus cuniculus).

A trial-by-trial, subject-by-subject analysis was conducted to determine whether generation of the conditioned response (CR) occurs on a continuous or all-or-none basis. Three groups of rabbits were trained on different partial reinforcement schedules with the conditioned stimulus presented alone on 10%, 30%, or 50%, respectively, of all trials. Plots of each rabbit's nictitating membrane movements revealed that their magnitude rose in a continuous fashion. Response growth during acquisition followed a sigmoidal curve, and the timing of CR-sized movements was largely stable throughout the experiment. The results are discussed with respect to alternative models of CR generation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Time-specific extinction and recovery of the rabbit's (Oryctolagus cuniculus) conditioned nictitating membrane response using mixed interstimulus intervals.

Extinguishing a conditioned response (CR) has entailed separating the conditioned stimulus (CS) from the unconditioned stimulus (US). This research reveals that elimination of the rabbit nictitating membrane response occurred during continuous CS-US pairings. Initial training contained a mixture of 2 CS-US interstimulus intervals (ISIs), 150 ms and 500 ms. The CRs showed double peaks, one for each ISI. When the 150-ms ISI was removed, its CR peak showed 2 hallmarks of extinction: a decline across sessions and spontaneous recovery between sessions. When a further stage of training was introduced with a distinctive CS using the 150-ms ISI, occasional tests of the original, extinguished CS revealed another hallmark of extinction, specifically, strong recovery of the 150-ms peak. These results support both abstract and cerebellar models of conditioning that encode the CS into a cascade of microstimuli, while challenging theories of extinction that rely on changes in CS processing, US representations, and contextual control. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evaluation of quicklime mixing for the remediation of petroleum contaminated soils

Quicklime mixing is an established solidification/stabilization technique to improve mechanical properties and immobilise contaminants in soils. This study examined the effects of quicklime mixing on the concentrations and leachability of petroleum hydrocarbon compounds, in two natural soils and on a number of artificial sand/kaolinite mixtures. Several independent variables, such as clay content, moisture content and quicklime content were considered in the study. After mixing the soils with the quicklime, pH, temperature, moisture content, Atterberg limits and concentrations of petroleum hydrocarbon compounds were determined on soil and leachate samples extracted from the treated soils. Significant decreases in concentrations of petroleum hydrocarbon compounds were measured in soils and leachates upon quicklime mixing, which may be explained by a number of mechanisms such as volatilization, degradation and encapsulation of the hydrocarbon compounds promoted by the quicklime mixing. The increase in temperature due to the exothermic hydration reaction of quicklime when in contact with porewater helps to volatilize the light compounds but may not be entirely responsible for their concentration decreases and for the decrease of heavy aliphatics and aromatics concentrations.     

Cemented products containing waste from mineral processing and bioleaching

The characteristics of cemented products ranging in initial consistency from ‘paste-like’ to ‘flowable’, relevant to paste backfill and backfill with controlled low strength materials (CLSM), respectively, were compared for mixes incorporating waste from pilot scale bioleaching of European refractory gold, copper and copper/nickel sulphide flotation concentrates. Compositional and structural properties were linked to mechanical strength, hydraulic conductivity and hydrolytic stability (leachability) in fabricated laboratory specimens containing sand, pulverised fuel ash, waste and Portland cement in the proportions 70, 15, 10 and 5, respectively, together with variable quantities of water. In some experiments, sand was replaced by flotation tailings.The results showed that mixtures containing 10% of waste with 15.0–37.5% water by mass gave cemented materials with unconfined compressive strength (UCS) in the range 0.4–3.0 MPa after 28 days of hardening, this range encompassing typical paste-fill and CLSM formulations. They also indicated formulations giving maximum UCS and retention of strength at higher water content in the presence of the (finer sized) waste. Hydraulic conductivity (10⁻⁷–10⁻⁹ m/s) was comparable to commercial CLSM. Chemical analysis indicated low levels of most toxic elements and correspondingly low diffusion leaching, thus reducing requirements for special lining or encapsulation procedures to avoid groundwater contamination. However, chromium leaching, for example, remained an issue, thus indicating a need for further development before regulatory acceptance and deployment in field applications can become feasible.The formulated materials are consistent in principle with a scheme of integrated waste management based on designed combinations of paste (for mine backfill), CLSM (for engineering foundation construction) and mineral bulk (for site landscape/soil restoration). In particular, they facilitate production of different materials for paste backfill and CLSM applications by judicious adjustment of water content.