Articles

Acidic mine water drainage (AMD) containing heavy metals from abandoned mine and spoil heaps is a major concern as it may generate significant surface water pollution. Research performed across the main Romanian closed mining perimeters revealed a high variability of chemico-physical characteristics of the AMD flows. Their chemical matrices show various ratios between specific chemical species. The efficiency of the AMD treatment is influenced by these ratios. The priority for the AMD treatment is the pH adjustment and heavy metals removal (most often done by oxidation and precipitation with alkaline reagents). One of the inherent issues, regardless of the treatment method, is represented by the high volumes of amorphous precipitates that are formed. After the gravitational separation – settling, these sludges can represent up to 35% (typically 10–25%) reported to the reaction tank outfow fow-rate. The solids content of the sludge is between 0.5 and 3.0% dry solids. As the generation of acidic mine water will continue for decades or even longer times, the improvement of the treatment methods is a must. Results of sludge densifcation tests using conventional high density sludge (HDS) method are discussed here, in correlation with the AMD source and the effects on the treated water quality.

Our research is an attempt to treat the municipal treatment plants influents in a three-step (anoxic, anaerobic and aerobic) pilot installation and photoinduced oxidation processes for xenobiotics removal. The advanced treated effluents could be reused as irrigation water (STAS 9450/88). Degradation of chlorobenzenes using various photoinduced oxidation processes such as UV/H2O2, UV/O3 and UV/H2O2/O3 was investigated. Comparative analyses of removal efficiency for trichlorobenzene (TCB) and hexachlorobenzene (HCB) taking into account tested operating parameters were performed. The operating parameters with significant infuence upon the removal efficiency of chlorobenzenes in homogeneous advanced oxidation processes (AOPs) are as following: micropollutants concentrations, reaction/irradiation time and oxidants doses (H2O2, O3). The selected variant, based on laboratory experiments could be used as tertiary treatment step for the municipal wastewater treatment plant, after verification of microbiological indicators, and the final effluent could be used in agricultural purposes – irrigation.

The focus of this study was to assess the treatment performance and granule progression over time within a continuous flow reactor. A continuous flow airlift reactor was seeded with aerobic granules from a laboratory scale sequencing batch reactor (SBR) and fed with dairy wastewater. Stereomicroscopic investigations showed that the granules maintained their integrity during the experimental period. Laser diffraction investigation showed proof of new granules formation with 100–500 μm diameter after only 2 weeks of operation. The treatment performances were satisfactory and more or less similar to the ones obtained from the SBR. Thus, removal efficiencies of 81–93% and 85–94% were observed for chemical oxygen demand and biological oxygen demand, respectively. The N-NHþ 4 was nitrified with removal efficiencies of 83–99% while the nitrate produced was simultaneously denitrified – highest nitrate concentration determined in the effluent was 4.2 mg/L. The removal efficiency of total nitrogen was between 52 and 80% depending on influent nitrogen load (39.3–76.2 mg/L). Phosphate removal efficiencies ranged between 65 and above 99% depending on the influent phosphate concentration, which varied between 11.2 and 28.3 mg/L.

This paper presents the application of treated industrial waste from alumina fabrication in the field of drinking water treatment as coagulant-flocculant reagent. Experimental tests emphasized the efficiency of recovered and purified sodium aluminate for surface water treatment. Three different flocculants (sodium aluminate, classic flocculant, polyaluminum chloride – PAC) at four aluminum doses were tested. Turbidity, total organic carbon (TOC), iron, manganese and sodium indicators were monitored. Similar removal efficiencies have been calculated for turbidity (>99%), iron (>99%), manganese (~80%), aluminum (94–98%) and 58 and 47% for TOC in case of recovered sodium aluminate and PAC, respectively. The application of recovered flocculant proved its efficiency for coagulation-flocculation treatment phase, which mean that could be used instead classical flocculant without any secondary pollution effects. Recovered sodium aluminate is a good flocculant for drinking water treatment with many other applications in the field of wastewater treatment.

With an ever increasing population, biological wastewater treatment process has a crucial importance in the world. Activated sludge can be defied as a microbial community and consists of free, flocculated and filamentous bacteria, protozoa, rotifers and other invertebrates. Many studies on the relationships between protozoa and physico-epresent an important indicator of the wastewater treatment process efficiency. At a certain concentration, heavy metals and other pollutants are toxic to most microorganisms. The protozoa community is represented by interacting organisms, including species that are sensitive, intermediate or resistant in their tolerance to pollutants. The focus of the research was to determine the effect of 3 metals (copper, chromium and zinc) on the activated sludge viability. Experiments were conducted in a continuous flow bioreactor (simulating the conditions of a WWTP) fed with real wastewater and inoculated with activated sludge obtained from a local wastewater treatment plant. Microscopic determinations were used to evaluate the diversity and dynamics of the activated sludge biocenosis community. The study emphasized that all three metals had a more or less impact on the protozoa community highlighting both the most sensitive and the most resistant species.

In Romania, drinking water is produced from surface water (60%) and groundwater (40%). The presence of inorganic compounds containing oxidizable nitrogen within groundwater sources (NH4+-N, NO2--N) at variable concentration levels in association with other pollutants /micropollutants from natural / anthropogenic origin asks for previous treatability studies before the setting-up of final treatment technology. The ones currently applied for NH4+-N oxidation involve use of chlorine for oxidation of specific pollutants (N-NH4+, S2- a.s.o.) and water disinfection. The high doses of chlorine required by NH4+-N “break point” chlorination process (Cl2:NH4 +-N weight ratio = 7.6÷15:1) are able to generate undesirable chlorinated by-products from which trihalomethanes are the only regulated for drinking water (MACTHM = 100 μg/L). The experimental results of treatability studies using chlorine as oxidant reagent for three groundwater sources located in Bucharest proximity containing among oxidizable pollutants: NH4+-N (≥1 mg/L), natural organic matter (DOC ≤ 3.5mg/L), Mn(II) ions are presented. The noncompliance aspects related to the quality of treated water (THMs concentration, residual chlorine, free and bound chlorine ratio a.s.o.) from groundwater sources containing high concentration NH4+-N impose replacement of classic treatment process based on chlorine chemical oxidation with other process (biological nitrification).

This paper is focusing on the first Romanian application of High Density Sludge (HDS) technology on a pilot scale for acid mine water treatment. The pilot HDS treatment plant (Geco variant) had a modular structure, very flexible in operation, able to operate in Low Density Sludge (LDS) and HDS systems, with three reactors, one flocculation tank and one settling tank. The main advantages of HDS technology were the lower amount of Ca(OH)2 (10% lower), lower volume of the sludge and the higher content of dry substance (15%) in the sludge.

This paper shows the results of laboratory scale tests for manganese removal from aqueous solutions and groundwater by sonolysis. Ultrasonic cavitation phenomena lead to active radicals generation able to transform soluble Mn (II) into insoluble species. The influence of initial manganese concentration, sonolysis time, oxidant (H2O2) and catalyst doses (Fe) in case of hybrid sonolysis, energy and amplitude of ultrasonic waves on manganese removal have been studied. Three categories of ultrasonic test were performed for synthetic solutions: direct sonolysis (US), hybrid system US + HO22 , Fenton sonolysis US + H2O2 + Fe. Based on preliminary results Fenton sonolysis was selected for experimental with groundwater (280µg Mn/L, 180 µg Fe initial / 1200 µg Fe/L after addition of ferrous sulfate, 12 mg C/L - dissolved organic carbon). Residual manganese concentration was 40µg Mn/L, below the limit (50µg Mn/L) for drinking water. The real pollution matrix of groundwater changes the optimal operational conditions significantly so, must be taking into consideration local characteristics during the year.

Using aerobic granular sludge for wastewater treatment has multiple advantages compared to conventional activated sludge systems, most important being the ability of simultaneous removal of the pollutants responsible for eutrophication: organic load, compounds of nitrogen (NH4+; NO3-) and phosphorus (PO43-). The advantages are currently exploited for developing the next generation of wastewater treatment systems while the identified limitations are approached by experimental and theoretical researches worldwide. The aim of the study consists in evaluating the possibility of predicting the system’s response to different changes in the influent wastewater loadings. The paper presents simulations results backed up by experimental data for pollutants removal efficiencies evaluation for a sequential batch reactor (SBR) with aerobic granular sludge. The mathematical model is based on the activated sludge model no. 3, which was updated by considering the simultaneous biological nitrification (NH4+àNO3-) and denitrification (NO3-àN2á) processes, thus complying with the biochemical reactions occurring in aerobic granular sludge sequential batch reactors. The model developed was validated by the experimental results obtained on a laboratory scale SBR monitored for over a month.

Mine water from abandoned mines and spoil heaps from closed mining perimeter may generate significant surface water pollution. In Romania there are tens of sources with moderate to high contamination. Mine water flows have to be treated to meet national regulation NTPA 001/2005 for discharging in surface waters as any wastewater in any water body: low limits for heavy metals, but also for species considered benign to a certain level – calcium, magnesium and sulfate. By lime precipitation treatment, some CaSO4 can be formed, lowering the [SO42–] level, but the limit for sulfate will not be achieved, because the concentration correlated to gypsum solubility exceeds it by roughly three times. Sulfate precipitation as ettringite is a robust multi-stage technology (ECOIND- WISUTEC 2007–2012), but the costs are not reasonably sustainable for long term. Some approaches for modified technological flow-sheets and laboratory test result for the valorisation of reactive aluminium sources (e.g. mine water aluminium or flows with wasted aluminium).