Outflow pH Research Articles

Autonomous real-time control for membrane capacitive deionization

Artificial intelligence has been employed to simulate and optimize the performance of membrane capacitive deionization (MCDI), an emerging ion separation process. However, a real-time control for optimal MCDI operation has not been investigated yet. In this study, we aimed to develop a reinforcement learning (RL)-based control model and investigate the model to find an energy-efficient MCDI operation strategy. To fulfill the objectives, we established three long-short term memory models to predict applied voltage, outflow pH, and outflow electrical conductivity. Also, four RL agents were trained to minimize outflow concentration and energy consumption simultaneously. Consequently, actor-critic (A2C) and proximal policy optimization (PPO2) achieved the ion separation goal (<0.8 mS/cm) as they determined the electrical current and pump speed to be low. Particularly, A2C kept the parameters consistent in charging MCDI, which caused lower energy consumption (0.0128 kWh/m3) than PPO2 (0.0363 kWh/m3). To understand the decision-making process of A2C, the Shapley additive explanation based on the decision tree model estimated the influence of input parameters on the control parameters. The results of this study demonstrate the feasibility of RL-based controls in MCDI operations. Thus, we expect that the RL-based control model can improve further and enhance the efficiency of water treatment technologies.

Long-term operational studies of lab-scale pumice-woodchip packed stormwater biofilters

ABSTRACTThe performance of three pumice-woodchip packed stormwater biofilter (PWSWBF) systems with three packing volume ratios of pumice to woodchip (1:2, 1:1 and 2:1) were compared. The results show that the PWSWBF system packed with a lower percentage of woodchip attained a higher removal efficiency of TCOD, TN, NH4–N and TP, whereas all three systems completely removed nitrate. The highest removal efficiencies for TCOD, TN, NH4–N, NO3–N and TP were 95%, 70%, 86%, 100% and 100%, respectively. In the biofilter with a lower percentage of woodchip, the pollutants that get removed through aerobic biological processes were removed more significantly, which is attributed to less oxygen depletion via woodchip decomposition, which is common under wet conditions. Nitrate was significantly removed via denitrification in all three systems, indicating that the woodchip that occupied one-third of the main media was sufficient for denitrification, and also that the oxygen condition inside the column was proper for denitrification to proceed. A smaller amount of woodchip as the packing material also mitigated the adverse effect of the release of organics from the media during the initial period. In addition, the system showed very good buffering capacity, in that the outflow pH was constant within the optimal range for microorganism growth.

Alternative processes of nitrogen removal from wastewater — startup of nitritation reactor

Abstract Efficient nitritation was tested in SBR with the aim to accumulate nitrites and to minimize nitrates production in reject wastewater with 500 mg L-1 (NH4 ++ NH3)-N and with different molar ratios of HCO3 -: (NH4 ++ NH3)-N (1.1-2.1). More than 80 % efficiency of nitritation and permanent inhibition of NOB were achieved at the ratios of 1.71.9 and at the loading of 0.16-0.6 kg (NH4 ++ NH3)-N m-3 d-1. Under these conditions, the outflow pH was in the range of 5.9-6.5, outflow c (NO2 - + HNO2)-N increased up to 400 mg L-1 and c (NO3 -)-N dropped below 50 mg L-1. Undissociated HNO2 was confirmed as the main inhibitor of NOB.

Evaluation of Solar Photosensitised River Water Treatment in the Caribbean

An economical supply of hygienic potable water is one of the most pressing public health issues facing developing countries in the Caribbean region today. This project investigates the performance of a novel solar photochemical reactor for disinfecting river water. The prototype photochemical reactor was designed, constructed, and tested for the microbiological degradation of faecal coliform present in River Water. The experiments evaluated the efficacy of two photosensitive dyes (malachite green and methylene blue) as agents for detoxification with concentrations ranging from 0.5 to 3.0 mg/L. The photochemical reactor operated in a single-pass mode and compared the disinfection rates with direct photolysis. The photosensitizers showed a high efficacy rate using natural sunlight with microbial reduction ranging from 97 to 99% for concentrations as low as 0.5 mg/L of dye. The sensitizers were found to be photobleaching and were very effective at lower concentrations (&lt;2.0 mg/L). Direct photolysis inactivation rate constants were 0.034 and 0.046 min−1, whilst degradation rates using methylene blue ranged from 0.057 to 0.088 min−1and for malachite green from 0.057 to 0.086 min−1, respectively. One-way ANOVA was tested between the inflow and outflow pH, as well as the degradation rates constants for both photosensitisers withP&gt;0.01. Post-solar disinfection included the use of a coconut fiber filter which polished the water removing residual dye concentrations and bacterial contaminants.

High-strength greywater treatment in compact hybrid filter systems with alternative substrates

Four parallel pilot-scale experimental filter systems were established in 2009 in order to study the treatment capacity of hydrated oil shale ash (an industrial by-product) and Filtralite® in compact highly loaded filter systems in order to reduce BOD and COD values and nutrient concentration in household greywater. The systems were tested at two different hydraulic loading rates over a nearly two-year period. All the Filtralite® systems performed significantly better than the oil shale ash system, showing a median COD reduction of 83–88%, whereas the system with 4–10mm crushed Filtralite® performed significantly better than others filled with Filtralite®. The oil shale ash system clearly outperformed the Filtralite® systems, with a median reduction of TP in the oil shale ash filter system of 89%, achieving a median effluent concentration of 0.55mgPL−1 compared to the respective 40–44% and 2.9–3.3mgPL−1 for Filtralite® systems. The median outflow pH values of the Filtralite® systems and oil shale ash system were ∼8.5 and ∼9, respectively. It was also noticeable that most of the organic matter, TSS and even TN and TP was removed in vertical flow (VF) filters. When operating the filter systems under ∼2.5 times higher loading rates, there were no significant differences between the removal efficiencies regarding the organic matter, TSS and TN removal, although the fluctuations of pollutant content in inflow were more distinctly reflected in the outflow values and concentrations. The study serves as a good basis for the development of a low-tech compact filter system for greywater treatment.

Performance of Pilot-Scale Sulfate-Reducing Bioreactors Treating Acidic Saline Water Under Semi-Arid Conditions

Groundwater drains used to manage saline watertables in the semi-arid zone of south-western Australia can discharge acidic saline water with high concentrations of metals to waterways. Mitigating the acidity impacts of the waters requires sulfate-reducing bioreactors capable of functioning under semi-arid conditions with limited source materials. Two simple pilot-scale bioreactor designs using straw and sheep manure mixtures were evaluated over several years. The bioreactors increased pH from 5.5 for 125–260 days, with concurrent evidence of sulfate reduction, >85% reductions in net acidity and >90% reductions in Al and most trace elements (e.g. Pb, Cu, Ni, Zn, Ce and La). When outflow pH 80% reduced over periods of 250 to >700 days. Rates of alkalinity generation initially exceeded 10 g CaCO3/m2/day in both bioreactors thereafter decreasing to >1–2 CaCO3/m2/day. Al and Fe retention was implicated in trace metal removal when pH < 5.5, mediated by biological alkalinity generation. High evaporation rates limited bioreactor function by restricting outflows with no benefits to alkalinity generation rates. This experiment showed that simple bioreactors can neutralise acidic waters and remove metals for short durations and show capacity for sustained reduction in acidity and metal concentrations over several years despite low alkalinity generation.

Migration and retention of dissolved iron in three mesocosm wetlands

Three mesocosm wetlands (250 cm × 100 cm × 100 cm) with different wetland plants ( Calamgrostis angustifolia, CA, Carex lasiocarpa, CL, and C. angustifolia/ C. lasiocarpa mixture, AL, respectively) and hydrologic regimes were set to test migration and retention of exogenous dissolved iron ((NH 4) 2Fe(SO 4) 2of 40 mg Fe(II) L −1) in the Sanjiang Plain Wetland in northeast China. The experiment was designed as two stages: open migration period (OMP) for 1.5 d and close retention period (CRP) for 28.5 d. Based on the outflow Fe(II) concentration during the OMP, retention efficiencies (RE) and iron retention fluxes adjusted by area (RF ad) in the three mesocosm wetlands were calculated, and the migration of iron were modeled using the first-order kinetic model. Outflow pH decreased gradually from a weak alkaline condition to a weak acid condition during the OMP, and then increased during the CRP, while outflow Eh and DO decreased during the experiment. The three mesocosm wetlands had considerable RE ranging from 75% to 98%, with the averaged RF ad of 4.31 ± 0.17, 4.20 ± 0.16, and 4.37 ± 0.13 g m −2 h −1 for CA, CL, and AL, respectively. The reduction conditions in the mesocosm wetlands developed after 4 d or 12 d and the former retained iron during the OMP became mobile and discharged primarily in the form of Fe(III). The first-order kinetic model could simulate the outflow concentration of dissolved iron during the OMP ( R 2 = 0.91, 0.69, and 0.68 for CA, CL, and AL, respectively), while the outflow dissolved iron during the CMP was difficult to model because the changed pH and Eh conditions in the mesocosm wetlands cause the former precipitated iron to be mobile after several days.

Effects of cerebrospinal fluid acidity on cerebral blood flow and autoregulation in rats.

Using a ventriculocisternal perfusion method, the effects of cerebrospinal fluid (CSF) acidity of nonrespiratory origin on cerebral blood flow (CBF) and autoregulation of CBF were investigated. Three groups (six rats each) were studied: one group of sham operated rats, one control group with ventriculocisternal perfusion at normal pH (mean inflow pH +/- SD, 7.42 +/- 0.02), and one experimental group with ventriculocisternal perfusion at low pH (mean inflow pH +/- SD, 6.81 +/- 0.01). CBF was measured by the intracarotid xenon 133 method. Autoregulation was studied by repetitive measurements of CBF during an initial increase and then stepwise reduction of mean arterial blood pressure (MABP). No difference in CBF was found between sham operated and control rats with unperturbed pH (mean cisternal outflow pH +/- SD, 7.42 +/- 0.03) of CSF), and autoregulation was intact in both groups. In the experimental group, the mean CBF +/- SD was increased by 58%, from 127 +/- 33 mL/(100 g.min) before ventriculocisternal perfusion to 201 +/- 54 mL/(100 g.min) (P <.00001) during perfusion with acid CSF (mean cisternal outflow pH +/- SD, 7.23 +/- 0.04). In this group, the relationship between CBF and MABP was linear, thus indicating disrupted autoregulation. In conclusion, CSF acidity significantly increases CBF and impairs autoregulation of CBF.

Ion input/output budgets for five wetlands constructed for acid coal mine drainage treatment

Five wetlands, each 6 m wide and 30 m long and containing 30 cm of an organic substrate (Sphagnum peat to which limestone and fertilizer were surface-applied on a quarterly basis, Sphagnum peat, sawdust, straw/manure, spent mushroom compost), were exposed to controlled inputs of acid coal mine drainage (AMD; pH 2.89, soluble Fe, Mn, and SO4 2− concentrations of 119, 19, and 3132 mg L−1, respectively) at a mean flow rate of 8513 L da−1 for 111 weeks, beginning in July of 1989. All wetlands were net sources, rather than sinks, for base cations (Ca2+, Mg2+, Na+, K+). The Sphagnum peat wetland was the least effective in treating the AMD, retaining 35% of the soluble Fe influx, but not retaining substantial H+, soluble Mn, soluble Al, SO4 2−, or acidity. The straw/manure and mushroom compost wetlands were the most effective in treating the AMD, retaining 53 and 67% of the H+ influx, 80 and 78% of the soluble Fe influx, 7 and 20% of the soluble Mn influx, 54 and 53% of the soluble Al influx, 15 and 11% of the SO4 2− influx, and 57 and 63% of the acidity influx. For these two wetlands especially, treatment effectiveness was substantially diminished during the cold winter months of January through March. Moreover, from March through July of the final year of the study, treatment effectiveness was minimal with outflow pH and concentrations of soluble Fe, Mn, Al, SO4 2− and acidity that were similar to inflow values. Decreases in treatment effectiveness over time appeared to be related to a decrease in the ability to counter the substantial acid load entering the wetlands in the AMD. Lime or limestone dissolution and bacterial dissimilatory sulfate reduction may have contributed substantially to pH improvement and acidity consumption in the straw/manure and mushroom compost wetlands, but after 2 years the cumulative input of acidity apparently had overwhelmed biotic and abiotic alkalinity generating mechanisms, as reflected in a progressive decrease in both substrate pH and abiotic acid neutralization capacity (ANC) over time, especially in the surface substrates. Also over time, effluent H+ and acidity concentrations became more like influent and H+ and acidity concentrations. Although samples of wetland interstitial water were not collected for chemical analysis, as substrate pH and ANC decreased and as influent and effluent water chemistry became more similar, it is likely that wetland interstitial water became progressively more acidic, potentially inhibiting bacterial processes that could contribute to effective treatment, favoring dissolution rather than formation of insoluble metal precipitates, and thereby contributing to the eventual failure of the wetlands to effectively treat the AMD. In general, when constructed wetlands are used to treat particularly acidic (pH<4) AMD, if abiotic and biotic alkalinity generation cannot balance the influent acid load, long-term effective treatment will not be achieved.

Snow chemistry in the central Sierra Nevada, California

Precipitation and snowpack basal outflow event samples were analyzed for pH and NO3 and SO4 concentrations at a site near Lake Tahoe, California. The seasonal minimum pH from basal outflow was synchronous with a rain-on-snow event in 1984. Outflow pH reflected the low ionic concentrations of precipitation at the site. There was no evidence for a pulse of acidified meltwater at this site either during a mid-February melt induced by high air temperatures in 1985 or during 1984 or 1985 main spring melt periods. During the mid-February 1985 melt, however, an alkalinity pulse occurred in basal outflow.

PH environmental of red cells in the spleen.

Intrasplenic pH in vivo was deduced from measurements on blood drained from cat spleen during contraction with the inflow occluded. The pH of blood in the red pulp is normally 7.20, but stasis or reduced flow through the pulp causes pH to fall toward 6.8. The splenic pulp contains blood of high hematocrit. To evaluate the role of buffering by the red cells themselves, intrasplenic p/ in red cell-free spleens was, therefore, estimated atering and leaving the spleen during red cell washout. At inflow pH less than 6.8 the outflow pH was raised, at inflow pH = 6.8 there was no change, b,t at inflow pH greater than 6.8 the outflow pH was lowered. These results indicate that the pH environment of red cells in the spleen results indicate that the pH environment of red cells in the spleen results from the interplay of two separate factors: i) pH-determining elements of the splenic tissue that buffer at 6.8, and ii) buffering provided by red cells passing through the pulp.