2-Chlorophenol consumption and its effect on the nitrifying sludge

The kinetic behavior of a nitrifying sludge exposed to 2-chlorophenol (2-CP) was evaluated in batch culture. The assays were performed using a stabilized nitrifying sludge. In control assays with (mg L(-1)): NH(4)(+)-N (100) and NaHCO(3)(-)-C (250), the substrates were consumed in 8h, the ammonium consumption efficiency was 99% and the NO(3)(-) yield higher than 0.9. When 5mg 2-CP-C L(-1) was added, it was transformed into an unidentified intermediate and the nitrifying efficiency decreased to 10%. Ammonium specific consumption rate diminished 95%, but the NO(3)(-) yield remained higher than 0.9. The biomass previously exposed to 2-CP was newly suspended with NH(4)(+)-N or NO(2)(-)-N in order to evaluate the ammonium and nitrite oxidizing processes. The consumption efficiencies and NO(3)(-) yields were similar to those obtained in control assays. However, the total time required for ammonium and nitrite consumption increased to 120 and 42 h, respectively. Specific consumption rates for NH(4)(+)-N and NO(2)(-)-N decreased by 95% and 83% respectively, compared to control assays. Thus, the previous contact to 2-CP had more influence on ammonium oxidizing process than the nitrite oxidizing process. These are the first evidences where a nitrifying sludge exposed to 2-CP are reported.     

Mechanism for sludge acidification in aerobic treatment of coking wastewater

This work was undertaken to investigate the cause of sludge acidification that led to disruption of the activated sludge process treating coking wastewater from a steel-making plant in Taiwan. An activated sludge reactor (ASR) with a working volume of 80 L was used as a model system to simulate the behavior of the real wastewater treatment process. Parameters that may cause acidification or inactivation of the sludge (NH(3), SCN(-), S(2)O(3)(2-) and CN(-)) were studied individually to examine for their effects on the performance of the ASR. The results show that high loading of NH(3), SCN(-) and CN(-) did not lead to pH decrease, while the ASR attained 85% COD removal and nearly 100% SCN degradation. In contrast, when the wastewater was supplemented with ca. 1,000 mg/L of S(2)O(3)(2-), the pH dropped to nearly 4.0 in 2 days and the COD and SCN removal yields were significantly lower (at 50 and 0-20%, respectively). Thus, overloading of S(2)O(3)(2-) was apparently a key factor causing sludge acidification. The results suggest that to ensure a normal functioning of the activated sludge, the influent S(2)O(3)(2-) concentration should be closely monitored and that the pH control of the ASR is indispensable when the S(2)O(3)(2-) loading is in excess.     

Chemical denitrification of water by zero-valent magnesium powder

A laboratory-scale study was conducted in batch mode to investigate the feasibility of using zero-valent magnesium (Mg(0)), for removal of nitrate from aqueous solution. Reaction pH, dose of Mg(0), initial nitrate concentration and temperature were considered variable parameters during the study. Strong acidic condition enhanced nitrate reduction and in absence of external proton addition, reaction pH increased rapidly above ten and insignificant nitrate removal (7-16%) was achieved. At Mg(0):NO(3)(-)-N molar ratio of 5.8 and controlled reaction pH of 2, 84% denitrification efficiency was achieved (initial NO(3)(-)-N 50 mg/L) under ambient temperature and pressure and total nitrogen removal was 70% with 3.2% and 10% conversion of initial NO(3)(-)-N to NO(2)(-)-N and NH(4)(+)-N, respectively. The reaction was first order with respect to nitrate concentration. Nitrate removal rate decreased with solution pH and increased linearly with Mg(0) dose. Nitrate removal was coupled with 96-100% removal of dissolved oxygen and 85-90% generation of soluble Mg(2+) ion. An activation energy (E(a)) of nitrate reduction over the temperature range of 10-50 degrees C was observed as 17.7 kJ mol(-1).     

Nitrification activity and community structure of nitrite-oxidizing bacteria in the bioreactors operated with addition of pharmaceuticals

Pharmaceuticals represent a group of the new emerging contaminants, which might influence microbial communities in the activated sludge. Nitrification activity and Nitrospira community structure in the small-scale reactors supplied with different concentrations (0, 50, 200, 500 μg L(-1)) of the selected pharmaceuticals (ibuprofen, naproxen, ketoprofen, diclofenac and clofibric acid) were evaluated. Ammonia removal was not influenced by selected pharmaceuticals. However, in the two reactors operated with 50 μg L(-1) of pharmaceuticals (R50 and R50P), the effluent concentration of N-(NO(2)(-)+NO(3)(-)) was significantly higher than in the other reactors. Nitrospira community structure was assessed by terminal restriction fragment length polymorphism (T-RFLP) and by cloning and sequencing of the partial genes for 16S rRNA. Nitrospira spp. were detected in all reactors. The two dominant T-RFs represented the sublineages I and II of the genus Nitrospira. Main shifts were observed in the reactors R50 and R50P, where the T-RF representing sublineage II was much higher as compared to the other reactors. Consistent with this, the Nitrospira sublineage II was detected only in the clone libraries from the reactors R50 and R50P. Our results suggest that the relative abundance of Nitrospira sublineage II could be related to the effluent N-(NO(2)(-)+NO(3)(-)) concentration.     

Photocatalytic degradation of C.I. Acid Red 27 by immobilized ZnO on glass plates in continuous-mode

The photocatalytic degradation of C.I. Acid Red 27 (AR27), an anionic monoazo dye of acid class, in aqueous solutions was investigated with immobilized ZnO catalyst on glass plates in a continuous-mode. In the slurry ZnO system the separation and recycling of the photocatalyst is practically difficult. Thus, ZnO was immobilized on solid supports to solve this problem. The removal percent increases with increasing the photoreactor volume and light intensity but it decreases when the flow rate is increased. With decreasing flow rate from 43 to 15mlmin(-1), the complete decolorization and degradation was obtained at around 748 and 1080cm(3) from photoreactor volume. The increase in the light intensity from 21.4 to 58.5Wm(-2) increases the decolorization from 23 to 57.6% and degradation from 17.5 to 37.8% for 374cm(3) of photoreactor volume. NH(4)(+), NO(3)(-), NO(2)(-) and SO(4)(2-) ions were analyzed as mineralization products of nitrogen and sulfur heteroatoms. Results showed that final concentration of SO(4)(2-) ions and N-containing mineralization products were less than the finally expected stoichiometric values. The positive slope of production of NH(4)(+), NO(3)(-) and NO(2)(-) shows that these compounds are initial products resulting directly from the initial attack on the nitrogen-to-nitrogen double bond (-NN-) of the azo dye.     

The effect of isosaccharinic acid (ISA) on the mobilization of metals in municipal solid waste incineration (MSWI) dry scrubber residue

Co-landfilling of incineration ash and cellulose might facilitate the alkaline degradation of cellulose. A major degradation product is isosaccharinic acid (ISA), a complexing agent for metals. The impact of ISA on the mobility of Pb, Zn, Cr, Cu and Cd from a municipal solid waste incineration dry scrubber residue was studied at laboratory using a reduced 2(5-1) factorial design. Factors investigated were the amount of calcium isosaccharinate (Ca(ISA)(2)), L/S ratio, temperature, contact time and type of atmosphere (N(2), air, O(2)). The effects of pH and Ca(ISA)(2) as well as other factors on the leaching of metals were quantified and modelled using multiple linear regression (alpha=0.05). Cd was excluded from the study since the concentrations were below the detection limit. The presence of Ca(ISA)(2) resulted in a higher leaching of Cu indicating complex formation. Ca(ISA)(2) alone had no effect on the leaching of Pb, Zn and Cr. A secondary effect on the mobilization was predicted to occur since Ca(ISA)(2) had a positive effect on the pH and the leaching of Pb, Zn and Cr increased with increasing pH. The leaching of Pb varied from 24 up to 66 wt.% of the total Pb amount (1.74+/-0.02 g(kgTS)(-1)) in the dry scrubber residue. The corresponding interval for Zn (7.29+/-0.07 g(kgTS)(-1)) and Cu (0.50+/-0.02 g(kgTS)(-1)) were 0.5-14 wt.% of Zn and 0.8-70wt.% of Cu. Maximum leaching of Cr (0.23+/-0.03 g(kgTS)(-1)) was 4.0 wt.%. At conditions similar to a compacted and covered landfill (4 degrees C, 7 days, 0 vol.% O(2)) the presence of ISA can increase the leaching of Cu from 2 to 46 wt.% if the amount of cellulose-based waste increases 20 times, from the ratio 1:100 to 1:5. As well, the leaching of Pb, Zn, and Cr can increase from 32 to 54 wt.% (Pb), 0.8-8.0 wt.% (Zn), and 0.5 to 4.0 wt.% (Cr) depending on the amount of cellulose and L/S ratio and pH value. Therefore, a risk (alpha=0.05) exists that higher amounts of metals are leached from landfills where cellulose-containing waste and ash are co-disposed. This corresponds to an additional 29 t of Pb and 17 t of Cu leached annually from a compacted and covered landfill in the north of Sweden.     

Trimethylamine (TMA) biofiltration and transformation in biofilters

Bioremoval of trimethylamine (TMA) in two three-stage biofilters packed with compost (A) and sludge (B), respectively, was investigated. Both biofilters were operated with an influent TMA concentration of 19.2-57.2mgm(-3) for 67 days. Results showed that all of the inlet TMA could be removed by both biofilters. However, removal efficiency and transformation of TMA in each section of both biofilters was different. In the Introduction section, TMA removal efficiency and maximum elimination capacity of the compost medium were greater than those of sludge medium under higher inlet TMA concentration. In comparison with biofilter A, considerably higher NH(3) concentrations in effluent of all three sections in biofilter B were observed after day 19. Although, NO(2)(-)-N concentration in each section of biofilter A was relatively lower, NO(3)(-)-N content in each section of biofilter A increased after day 26, especially in the Materials and method section which increased remarkably due to a lesser amount of TMA and higher ammonia oxidation and nitrification in compost medium. In contrast, neither NO(2)(-)-N nor NO(3)(-)-N were detected in either section of biofilter B at any time throughout the course of the experiment. The cumulative results indicated that compost is more favorable for the growth of TMA-degrading and nitrifying bacteria as compared to the sludge and could be a highly suitable packing material for biodegradation and transformation of TMA.     

Negative chemical ionization GC/MS determination of nitrite and nitrate in seawater using exact matching double spike isotope dilution and derivatization with triethyloxonium tetrafluoroborate

The alkylation of nitrite and nitrate by triethyloxonium tetrafluoroborate allows determination of their ethyl esters by headspace gas chromatography/mass spectrometry (GC/MS). In the present study, significant improvement in analytical performance is achieved using negative chemical ionization providing detection limits of 150 ng/L for NO(2)(-) and 600 ng/L for NO(3)(-), an order of magnitude better than those achieved using electron impact ionization. The derivatization procedure was optimized and alkaline conditions adopted to minimize conversion of nitrite to nitrate (determined to be 0.07% at 100 mg/L NO(2)(-)) and to avoid the exchange of oxygen between the analytes and the solvent (water). Quantitation entails use of isotopically enriched standards (N(18)O(2)(-) and (15)NO(3)(-)), which also permits monitoring of potential conversion from nitrite to nitrate during the analysis (double spike isotope dilution).     

Assessing arsenic leachability from pulverized cement concrete produced from arsenic-laden solid CalSiCo-sludge

Synthetically prepared arsenic-laden CalSiCo-sludge was converted to pulverized cement concrete (PCC) using solidification/stabilization technology with cement. Batch leaching experiments were conducted to estimate the leaching of As(III) and As(V) from the CalSiCo-sludge as well as from the PCC. The leaching of As(III) and As(V) was found to be the function of time, pH and concentration of anions such as Cl(-), NO(3)(-), and SO(4)(2-) present in the extraction fluid. It is observed that from the CalSiCo-sludge the leaching of As(III) is >0.05mg/l (which is above the permissible limit for arsenic in drinking water) at any pH. But in case of As(V) the leaching is >0.05mg/l only at pH>8 and at pH<4. It is noted that maximum leaching occurs when the extraction liquid contains Cl(-). In contrary, NO(3)(-) and SO(4)(2-) have negligible effect on arsenic leaching from the CalSiCo-sludge. Extraction tests were carried out to determine the maximum leachable concentration under the chosen conditions of leaching medium and leaching time. Leaching of As(III) and As(V) from exhausted arsenic-laden CalSiCo-sludge and from PCC was carried out in both tap water and rain water. It was noticed that tap water has no effect in leaching of arsenic from CalSiCo-sludge but rain water causes significant amount of leaching, which is mostly due to pH effect. However, in all cases the leaching of As(III) was more than that of As(V). When compared with CalSiCo-sludge PCC showed negligible leaching of arsenic. It was noticed further that the variation of 28 days compressive strength was within 15% of the original strength after replacing 35% cement with exhausted CalSiCo-sludge.     

Phosphate removal using sludge from fuller's earth production

This study assesses the phosphate removal capacity and mechanism of precipitation or adsorption from aqueous solutions in batch experiments by an industrial sludge containing gypsum (CaSO(4).2H(2)O) obtained as a by-product from a fuller's earth process. The potential capacity for phosphate removal was tested using various solution concentrations, pH values, reaction times, and amount of sludge. The maximum phosphate adsorption capacity calculated using the Langmuir equation was 2.0 g kg(-1). The pH for the maximum adsorption by the sludge was neutral to alkaline (pH 7-12). Over 99% of phosphate was removed from a phosphate solution of 30 mg L(-1) using 0.15 g of sludge in a 9-h reaction. Sulfate (SO(4)(2-)) concentration increased with increasing initial phosphate concentration, possibly because of dissolution of gypsum and adsorption of both sulfate and phosphate. At high phosphate concentration (>1000 mg L(-1)), relative constant concentration of Ca(2+) was not consistent with adsorption of the most important phosphate removal mechanism. Results suggest that precipitation of calcium phosphate is principally responsible for phosphate removal under its high concentration. Agglomerated precipitate in the reaction sludge was observed by SEM and identified as brushite (CaHPO(4).2H(2)O) by XRD, FT-IR, and DTA. Based on thermodynamic considerations, it is suggested that the brushite will readily transform to more stable phases, such as hydroxyapatite (Ca(5)(PO(4))(3).OH).     

Anaerobic ammonia removal in presence of organic matter: a novel route

This study describes the feasibility of anaerobic ammonia removal process in presence of organic matter. Different sources of biomass collected from diverse eco-systems containing ammonia and organic matter (OM) were screened for potential anaerobic ammonia removal. Sequential batch studies confirmed the possibility of anaerobic ammonia removal in presence of OM, but ammonia was oxidized anoxically to nitrate (at oxidation reduction potential; ORP=-248+/-25 mV) by an unknown mechanism unlike in the reported anammox process. The oxygen required for oxidation of ammonia might have been generated through catalase enzymatic activity of facultative anaerobes in mixed culture. The oxygen generation possibility by catalase enzyme route was demonstrated. Among the inorganic electron acceptors (NO(2)(-), NO(3)(-) and SO(4)(2-)) studied, NO(2)(-) was found to be most effective in total nitrogen removal. Denitrification by the developed culture was much effective and faster compared to ammonia oxidation. The results of this study show that anaerobic ammonia removal is feasible in presence of OM. The novel nitrogen removal route is hypothesized as enzymatic anoxic oxidation of NH(4)(+) to NO(3)(-), followed by denitrification via autotrophic and/or heterotrophic routes. The results of batch study were confirmed in continuous reactor operation.     

Development of enhanced sulphidogenesis process for the treatment of wastewater having low COD/SO(4)(2-) ratio

An upflow hybrid sulphidogenesis reactor of 1.75 L volume was developed (at oxidation-reduction potential (ORP)=-225+/-25 mV) using flocculent extended aeration process sludge (selected based on screening study at COD/SO(4)(2-) ratio=1) for enhanced sulphidogenesis and COD removal. The reactor was subjected to various loading rate studies at a hydraulic retention time (HRT) of 1 day with COD/SO(4)(2-) ratio of 1.3. At loading rate of 2.5 kg COD/(m(3)day), excellent performance with more than 97% removal of sulphate was achieved within bottom 40% volume of the reactor. At a higher loading rate of 3.75 kg COD/(m(3)day), there was a decrease in both sulphate (70-75%) and COD (50%) removal efficiencies. A controlled and continuous air injection (0.19 L/(L min)) given at 40% volume of the reactor affected sulphide oxidation inside the reactor and enhanced the sulphate reduction in the reactor. The specific sulphate reduction capacity of mixed culture drawn from the bottom part of the reactor was 0.35 kg SO(4)(2-)/(kg VSS day). The results of this study showed that enhanced sulphidogenesis with sulphide inhibition control can maintain sulphate-reducing bacteria (SRB) in anaerobic reactor at low COD/SO(4)(2-) ratios between 1 and 2, with efficient simultaneous removal of COD and SO(4)(2-). The sulphide generated in the system can be recovered as elemental sulphur and/or oxidized back to sulphate.     

Nitrate removal by Thiobacillus denitrificans immobilized on poly(vinyl alcohol) carriers

Nitrate contamination is becoming a widespread environmental problem, and autotrophic denitrification with Thiobacillus denitrificans is a promising process considering efficiency, cost and maintenance. The denitrification efficiencies of T. denitrificans were compared in batch reactors between free cells and cells immobilized on polyvinyl alcohol (PVA) carriers made with thrice freezing/thawing and boric acid methods. The results indicated that the free cell reactor of T. denitrificans added with 10% (v/v) of PVA carrier made by thrice freezing/thawing (PVA-TFT) exhibited faster in S(2)O(3)(2-)-S consumption, SO(4)(2-) generation, and NO(3)(-)-N denitrification, with corresponding values being 165 mg (S(2)O(3)(2-)-S)/L.d, 491 mg (SO(4)(2-))/Ld, and 44 mg (NO(3)(-)-N)/Ld, which were increased by 50%, 61%, and 57% respectively compared to the control reactor with only free cells. Inhibition of denitrification by accumulated SO(4)(2-) in PVA-TFT reactor appeared at the concentration of approximately 6000 mg (SO(4)(2-))/L, and 75% of NO(3)(-)-N removal efficiency was achieved after 12d operation under the condition of initial 700 mg/L NO(3)(-)-N concentration.     

Performance enhancement of batch aerobic digesters via addition of digested sludge

The impact of the feed sludge (FS) concentration and addition of digested sludge (DS) to an aerobic digester was evaluated with respect to its capability for removal of the total suspended solids (TSS) and volatile suspended solids (VSS). The aerobic digesters, which operated in a batch mode at constant temperature and mixing rate, were initially filled with FS to 25%, 50%, 75%, and 100% of the reactor's volume. The remaining volume of the reactor was occupied by the DS, having DS/FS ratio of 3, 1, 1/3, and 0. Analysis of the experimental data showed that in the absence of DS, TSS, and VSS destruction rates are very small; however, increasing DS/FS ratio from 1/3 to 3 results in 74-77% increase in VSS and TSS destruction, respectively. The increase of the DS/FS ratio associated with increased ratio of the measured viable biomass (Cc) to VSS concentration (Xv) suggested that DS serves as the source of viable cell mass needed for degradation of organic solids. Assuming pseudo-first-order kinetics, it was shown that while organic solid destruction rate constants (k) are inversely related to initial concentrations of sludge, their values increase with increasing DS/FS ratios.     

Landfill leachate treatment with a novel process: anaerobic ammonium oxidation (Anammox) combined with soil infiltration system

A novel combined process was proposed to treat municipal landfill leachate with high concentrations of ammonium and organics. This process consisted of a partial nitritation reactor (PNR), an anaerobic ammonium oxidation (Anammox) reactor (AR) and two underground soil infiltration systems (USIS-1 and USIS-2). Based on the optimum operating conditions obtained from batch tests of individual unit, the combined process was continuously operated on a bench scale for 166 days. Partial nitritation was performed in a fixed bio-film reactor (PNR, working volume=12 L). Ammonium nitrogen-loading rate (Nv) and DO were combined to monitor partial nitritation, and at T=30+/-1 degrees C, Nv=0.27-1.2 kg/(m3.d), DO=0.8-2.3 mg/L, the ratios of nitrite nitrogen (NO2--N) to ammonium nitrogen (NH4+-N) were successfully kept close to 1.0-1.3 in the effluent. Nitrate nitrogen (NO3--N) less than 43 mg/L was observed. The effluent of PNR was ideally suited as influent of AR. Sixty-nine percent CODcr from the raw leachate was degraded in the PNR. Anammox was carried out in a fixed bio-film reactor (AR, working volume=36 L). At T=30+/-1 degrees C, Nv=0.06-0.11 kg/(m3.d), about 60% NH4+-N and 64% NO2--N in the influent of AR were simultaneously removed. Inhibition of high-strength NO2--N (up to 1011 mg/L) should be responsible for the low removal rate of nitrogen. About 35% aquatic humic substance (AHS) was degraded in the AR. With the same working volume (200 L), USIS-1 and USIS-2 were alternately performed to treat the effluent from AR at one cycle of about 30 days. At hydraulic loading rate (HLR)=0.02-0.04 m3/m3.d, pollutant loading rates (PLR)=NH4+-N相似文献   

Coagulation/flocculation process and sludge conditioning in beverage industrial wastewater treatment

Attempts were made in this study to examine the effectiveness of coagulation and flocculation process using ferric chloride and polyelectrolyte (non-ionic polyacrylamide) for the treatment of beverage industrial wastewater. Removal of organic matter (expressed as chemical oxygen demand, COD), total phosphorus (TP) and total suspended solid (TSS) using ferric chloride and organic polyelectrolyte during coagulation/flocculation process were investigated. Also, the optimum conditions for coagulation/flocculation process, such as coagulant dosage, polyelectrolyte dosage, and pH of solution were investigated using jar-test experiment. The effect of different dosages of polyelectrolyte in combination with coagulant was also studied. The results revealed that in the range of pH tested, the optimal operating pH was 9. Percentage removals of 73, 95 and 97 for COD, TP and TSS, respectively, were achieved by the addition of 300mg/L FeCl(3).6H(2)O, whereas 91, 99 and 97% removal of COD, TP and TSS, respectively, were achieved with the addition of 25mg/L polyelectrolyte to 100mg/L ferric chloride. The volume of sludge produced, when ferric chloride was used solely, was higher compared to the use of combination of polyelectrolyte and FeCl(3).6H(2)0. The combined use of coagulant and polyelectrolyte resulted in the production of sludge volume with reduction of 60% of the amount produced, when coagulant was solely used for the treatment. It can be concluded from this study that coagulation/flocculation may be a useful pre-treatment process for beverage industrial wastewater prior to biological treatment.     

Kinetic analysis of phenol, thiocyanate and ammonia-nitrogen removals in an anaerobic-anoxic-aerobic moving bed bioreactor system

A simulated wastewater containing phenol (2500 mg/L), thiocyanate and ammonia-nitrogen (500 mg/L) was treated in an anaerobic (R1)-anoxic (R2)-aerobic (R3) moving bed biofilm reactor system at different hydraulic retention time (HRT) intervals (total HRT 3-8 days, R1: 1.5-4 days; R2: 0.75-2 days and R3: 0.75-2 days) and feed thiocyanate (SCN(-)) concentrations (110-600 mg/L) to determine substrate removal kinetics. In R1, phenol and COD reduction and specific methanogenic activity were inhibited due to the increase of SCN(-) in feed. Bhatia et al. model having inbuilt provision of process inhibition described the kinetics of COD and phenol utilization with maximum utilization rates of 0.398 day(-1) and 0.486 day(-1), respectively. In R2 and R3 modified Stover-Kincannon model was suitable to describe substrate utilization. In R2 respective maximum SCN(-), phenol, COD and NO(3)(-)-N utilization rates were 0.23, 5.28, 37.7 and 11.82 g/L day, respectively. In aerobic reactor R3, COD, SCN(-) and NH(4)(+)-N removal rates were, respectively, 10.53, 1.89, and 2.17 g/L day. The minimum total HRT of three-stage system was recommended as 4 days.     

Effect of NaOH on the vitrification process of waste Ni-Cr sludge

This study investigated the effect of NaOH on the vitrification of electroplating sludge. Ni, the major metal in the electroplating sludge, is the target for recovery in the vitrification. Sludge and encapsulation materials (dolomite, limestone, and cullet) were mixed and various amounts of NaOH were added to serve as a glass modifier and a flux. A vitrification process at 1450 °C separated the molten specimens into slag and ingot. The composition, crystalline characteristics, and leaching characteristics of samples were measured. The results indicate that the recovery of Ni is optimal with a 10% NaOH mass ratio; the recoveries of Fe, Cr, Zn, Cu, and Mn all exhibited similar trends. The results of the toxicity characteristic leaching procedure (TCLP) show that leaching characteristics of the slag meet the requirements of regulation in Taiwan. In addition, a semi-quantitative X-ray diffraction analysis revealed that the main crystalline phase of slag changed from Ca(3)(Si(3)O(9)) to Na(4)Ca(4)(Si(6)O(18)) with a NaOH mass ratio of over 15%, because the Ca(2+) ions were replaced with Na(+) ions during the vitrification process. Na(4)Ca(4)(Si(6)O(18)), a complex mineral which hinders the mobility of metals, accounts for the decrease of metal recovery.     

Anaerobic stabilisation of sludge produced during municipal wastewater treatment by electrocoagulation

Anaerobic digestion of sludge from small electrocoagulation wastewater treatment plant (SEWWTP) is described. The sludge for digestion (SEWWTP sludge) was taken from pilot-scale SEWWTP with the capacity of about 200-population equivalent (25 m3 of municipal wastewater per day). Due to the technology of wastewater treatment, the characteristics of SEWWTP sludge was different from sludge produced in conventional mechanical-biological wastewater treatment plant. Therefore, experiments were focused on possibilities of anaerobic sludge digestion and determination of conditions and parameters (amount and quality of the sludge, biogas production, etc.). Average COD removal efficiency in the pilot-scale SEWWTP exceeded 80%. Organic content of excess sludge (volatile suspended solids (VSS)) was in the range of 52.1-59.2% (these values are much lower compared to VSS content in raw sludge from conventional municipal wastewater treatment plant, where VSS is about 75%). Biogas production from anaerobic digestion of SEWWTP sludge was approximately three times lower compared to standard production in conventional municipal wastewater treatment plant. Low pH (6.5-6.7), high concentration of iron (up to 1400 mg/L) and aluminium (up to 1300 mg/L) and very low (almost zero) concentration of dissolved phosphorus in sludge water were the main factors limiting the rate of anaerobic processes. Based on these results, anaerobic digestion of SEWWTP sludge was not recommended as an appropriate stabilisation method.     

Discoloration and detoxicification of a Congo red dye solution by means of ozone treatment for a possible water reuse

The objective of this study was to investigate the degradation and mineralization of an azo-dye, the Congo red, in aqueous solutions using ozone. Phytotoxicity and the inhibitory effects on the microbial activity of the raw and the ozonated solutions were also carried out with the aim of water reuse and environment protection. Decolorization of the aqueous solutions, disappearance of the parent compound, chemical oxygen demand (COD) and total organic carbon (TOC) removal were the main parameters monitored in this study. To control the mineralization of the Congo red, pH of the ozonated solution and heteroatoms released from the mother molecule such NH(4)(+), NO(3)(-) and SO(4)(2-) were determined. It was concluded that ozone by itself is strong enough to decolorize these aqueous solutions in the early stage of the oxidation process. Nonetheless, efficient mineralization had not been achieved. Significant drops in COD (54%) were registered. The extent of TOC removal was about 32%. Sulfur heteroatom was totally oxidized to SO(4)(2-) ions while the central -NN- azo ring was partially converted to NH(4)(+) and NO(3)(-). Results of the kinetic studies showed that ozonation of the selected molecule was a pseudo-first-order reaction with respect to dye concentration. The obtained results also demonstrate that ozone process reduced the phytotoxicity of the raw solution and enhanced the biodegradability of the treated azo-dyes-wastewater. Hence, this show that ozone remains one of the effective technologies for the discoloration and the detoxification of organic dyes in wastewater.