Water treatment sludge for phosphate removal from the effluent of UASB reactor treating municipal wastewater

Aluminium-based water treatment sludge was used as a coagulant for removing/recovering phosphate from the effluent of upflow anaerobic sludge blanket (UASB) reactor treating municipal wastewater. The effect of three variables, namely sludge dose, initial pH and fresh coagulant (poly-aluminium chloride, PACl) dose was studied using response surface methodology. About 87% phosphate removal could be obtained at the optimum conditions of sludge dose 13.8 g/L, initial pH 6, and fresh PACl dose 5.8 mg Al/L. In order to achieve a similar phosphate removal, a dose in the range of 30–40 mg Al/L of fresh PACl was required. The results suggest that water treatment sludge can be reused as a coagulant for post-treatment of UASB reactor effluent treating municipal wastewater and can be considered as a promising alternative for removing phosphate which can substantially reduce the consumption of fresh PACl. The sludge generated during this process could potentially be used in land application which results in recycling of phosphate.     

Drop in dry mass and organic substance content in the process of autothermal thermophilic aerobic digestion

This paper presents the results of a study of a sludge subjected to the (ATAD) process – Autothermal Thermophilic Aerobic Digestion occurring in a two-stage installation operated in a municipal wastewater treatment plant in Olecko, Poland. The study of the sludge and the analysis of obtained results were conducted over 2011 and 2014. The subject of the study was a thickened sludge in an intermediate tank from which it was next transferred to facility reactors. The stabilization of processed sludge was evaluated analyzing the change in the dry mass (DS) content in the sludge. Measurements were carried out in thickened sludge samples and after the ATAD process. Collected results were then subjected to a statistical analysis and it was determined to which extent as resulted from the subject process the dry mass and the dry organic mass (VS) content was changing in the sludge. Also, it was analyzed how the oxygen chemical demand (COD) was changing. The dry mass content in the thickened sludge was from 60 g/l to 160 g/l. After the process, this amount was from 35 to 76 g/l. Similarly, the organic mass content in a dry sludge mass changed from initial values within a range of 44–135 g/l to 23–60 g/l after the ATAD process. Also, the organic substance content expressed as COD decreased from 80 to 467 g O₂/l in a thickened sludge to 51–261 g O₂/l in the sludge after the process. The article presents conclusions from the result of the conducted study as well as personal experience.     

Coupling of polyhydroxyalkanoate production with volatile fatty acid from food wastes and excess sludge

In this paper, the synthesis of polyhydroxyalkanoates (PHAs) by activated sludge with aerobic dynamic feeding process was conducted in a sequencing batch reactor by using food wastes and excess sludge fermentation liquid as the carbon source. The volatile fatty acids (VFAs) in the fermentation liquid were divided into even-numbered (acetic and butyric acid) and odd-numbered (propionic and valeric acid). The experiments conducted by central-composite design (CCD) showed that the pH could significantly affect the ratio of even-numbered to odd-numbered VFAs. Statistical analysis indicated a positive correlation (R² = 0.97, P < 0.05) between the consumption of even-numbered VFAs and the synthesized of PHB, while the consumption of odd-numbered VFAs were correlated with the synthesized PHV. By controlling the ratio of even-numbered to odd-numbered VFAs, the contents of PHV in the PHAs could be controlled within the range of 22–30%. When fermentative VFAs were used as the substrate for the synthesis of PHAs, the microbial synthesis of PHA and biomass was higher than that mixture of analytically pure acids was used. These results are of vital significance for the comprehensive utilization of solid wastes.     

Disintegration of waste activated sludge by different applications of Fenton process

Oxidative disintegration of municipal waste activated sludge (WAS) using conventional Fenton (Fe²⁺ + H₂O₂, CFP) and Fenton type (Fe⁰ + H₂O₂, FTP) processes was investigated and compared in terms of the efficiency of sludge disintegration and enhancement of anaerobic biodegradability. The influences of different operational variables namely sludge pH, initial concentration of Fe²⁺ or Fe⁰, and H₂O₂ were studied in detail. The optimum conditions have been found as catalyst iron dosage = 4 g/kg TS, H₂O₂ dosage = 40 g/kg TS and pH = 3 within 1 h oxidation period for both CFP and FTP. Kinetics studies were performed under optimal conditions. It was determined that the sludge disintegration was happened in two stages by both processes: rapid and subsequent slow disintegration stages and rapid sludge disintegration stage can be described by a zero-order kinetic model. The effects of oxidative sludge disintegration under the optimum conditions on anaerobic digestion were experienced with biochemical methane potential (BMP) assay in batch anaerobic reactors. Total methane production in the CFP and FTP pre-treated reactors increased by 26.9% and 38.0%, relative to the untreated reactor (digested the raw WAS). Furthermore, the total chemical oxygen demand reductions in the pre-treated reactors were improved as well.     

Partial nitritation of landfill leachate with varying influent composition under intermittent aeration conditions

The start-up and operation of a partial nitritation sequencing batch reactor for the treatment of landfill leachate were carried out on intermittent aeration mode. Partial nitrite accumulation was established in 15 days after the mode was changed from continuous aeration to intermittent aeration. Despite the varying influent composition, partial nitritation could be maintained by adjusting the hydraulic retention time (HRT) and the air flow rate. An increase in the air flow rate together with a decrease in air off duration can improve the partial nitritation capacity and eventually result in the development of granular sludge with fine diameters. A nitrogen loading rate of 0.71 ± 0.14 kg/m³/d and a COD removal rate of 2.21 ± 0.13 kg/m³/d were achieved under the conditions of an air flow rate of 19.36 ± 1.71 m³ air/m³/h and an air on/off duration of 1.5 min/0.7 min. When the ratio of total air flux (TAF) to the influent loading rate (ILR) was controlled at the range of 163–256 m³ air/kg COD, a stable effluent NO₃^?–N/NO_x^?–N (NO₂^?–N plus NO₃^?–N) ratio below 13% was achieved. Interestingly, the effluent pH was found to be a good indicator of the effluent NO₂^?–N/NH₄⁺–N ratio, which is an essential parameter for a subsequent anaerobic ammonium oxidation (Anammox) reactor.     

Pretreatment of municipal landfill leachate by a combined process

Biodegradability enhancement of landfill leachate using air stripping followed by coagulation/ultrafiltration (UF) processes was introduced. The air stripping process obtained a removal efficiency of 88.6% for ammonia nitrogen (NH₄–N) at air-to-liquid ratio of 3500 (pH 11) for stripping 18 h. The single coagulation process increased BOD/COD ratio by 0.089 with the FeCl₃ dosage of 570 mg l^?1 at pH 7.0, and the single UF process increased the BOD/COD ratio to 0.311 from 0.049. However, the combined process of coagulation/UF increased the BOD/COD ratio from 0.049 to 0.43, and the final biological oxygen demand (BOD), chemical oxygen demand (COD), NH₄–N and colour of leachate were 1223.6 mg l^?1, 2845.5 mg l^?1, 145.1 mg l^?1 and 2056.8, respectively, when 3 kDa molecular weight cut-off (MWCO) membrane was used at the operating pressure 0.7 MPa. In ultrafiltration process, the average solution flux (J_V), concentration multiple (M_C) and retention rate (R) for COD was 107.3 l m^?2 h^?1, 6.3% and 84.2%, respectively.     

Decolorization of synthetic Methyl Orange wastewater by electrocoagulation with periodic reversal of electrodes and optimization by RSM

Treatment of Methyl Orange (MO), an azo dye, synthetic wastewater by electrocoagulation with periodic reversal of the electrodes (PREC) was examined. Response Surface Methodology (RSM) was used to optimize the influence of experimental conditions for color removal (CR), energy consumption (ENC), electrode consumption (ELC) and sludge production (SP) per kg MO removed (kg(MO_r)) with optimal conditions being found to be pH 7.4, solution conductivity (к) 9.4 mS cm⁻¹, cell voltage (U) 4.4 V, current density (j) 185 mA cm⁻², electrocoagulation time (T) 14 min, cycle of periodic reversal of electrodes (t) 15 s, inter-electrode distance (d) 3.5 cm and initial MO concentration of 125 mg L⁻¹. Under these conditions, 97 ± 2% color was removed and ENC, ELC and SP were 44 ± 3 kWh kg(MO_r)⁻¹, 4.1 ± 0.2 kg(Al) kg(MO_r)⁻¹ and 17.2 ± 0.9 kg(sludge) kg(MO_r)⁻¹, respectively. With the enhanced electrochemical efficiency resulting from the periodic electrode reversal, the coefficients of increased resistance and decreased current density between the two electrodes in the PREC setup were 2.48 × 10⁻⁴ Ω cm⁻² min⁻¹ and 0.29 mA cm⁻² min⁻¹, respectively, as compared to 7.72 × 10⁻⁴ Ω cm⁻² min⁻¹ and 0.79 mA cm⁻² min⁻¹ as measured for the traditional electrocoagulation process. The rate constant of decolorization was also enhanced by 20.4% from 0.152 min⁻¹ in the traditional electrocoagulation process to 0.183 min⁻¹ in the PREC process. These performance characteristics indicate that the PREC approach may be more promising in terms of practical application, as a cost-effective treatment, than conventional electrocoagulation for textile dye removals.     

Removal mechanism of trace oxytetracycline by aerobic sludge

To investigate the mechanism of removal of selected pharmaceuticals in activated sludge systems, laboratory-scale batch experiments were conducted to assess the adsorption and degradation behavior of trace oxytetracycline (OTC). The adsorption equilibrium of OTC was observed in 30 min and the adsorption process could be well described by a pseudo-second-order model with a rate of 0.362 L μg^?1 min^?1. The OTC adsorption rate decreased with increasing temperature and could be fitted by the Freundlich isotherm. The linear partition coefficients (K_d) were 1.19, 0.999, and 0.841 L g^?1 at temperatures of 15, 20, and 25 °C, respectively. Thermodynamic analysis revealed that the adsorption of OTC onto the inactivated sludge was spontaneous (ΔG = ?16.7 to ?17.0 kJ mol^?1), enthalpy-driven (ΔH = ?24.9 kJ mol^?1), entropy-retarded (ΔS = ?27.4 J (mol K)^?1), and predominantly a physical adsorption.     

Effects of heavy metals on planting watercress in kailyard soil amended by adding compost of sewage sludge

Mixture of sewage sludge with organic garbage was alternatively composted by aerobic and anaerobic technology for 60 days. A basin-scale experiment was performed by planting watercress with kailyard (KY) soil amended with the compost. The results show that average total organic carbon (TOC) increases from 98.45% to 787.69%, and average total nitrogen (TN), total phosphorus (TP) and total potassium (TK) increases to 98.53%, 27.34%, and 41.62%, respectively. The results of watercress in 6 pot experiments with a control treatment show that biomass production increases from 76.47% to 312.00% with the increase of addition of compost from 50 g to 150 g per pot but decreases from 312.00% to 102.29% with the addition of compost to soil and further increases from 150 g to 400 g per pot. The optimal amount of compost added to KY soil is 0.4 g of compost 1 kg of KY soil. Heavy metals accumulated by watercress demonstrate that Cu, Ni, Cd, Pb, Cr, Zn in the crop are much lower than the limited levels of Chinese criteria for vegetables. KY soil is proper to be amended with compost of sewage sludge without threat of bio-magnification of heavy metals to planting watercress.     

7 mT static magnetic exposure enhanced synthesis of poly-3-hydroxybutyrate by activated sludge at low temperature and high acetate concentration

The effect of 7 mT (milliTesla) SMF (static magnetic field) on poly-3-hydroxybutyrate (PHB) production was studied at an acetate concentration of 260 Cmmol l^?1 and temperature of 10 °C. The SMF decreased the specific acetate uptake rate by 29%, but increased the maximum PHB content and the yield of PHB on acetate by 32 and 28% respectively. The ratio q_P/(q_S ? q_P), which described specific PHB production rate over the difference between specific acetate uptake rate and specific PHB production rate, was introduced for evaluation of the ratio of carbon flux into PHB synthesis and into the TCA (tricarboxylic acid) cycle. This value reached 2.3 when activated sludge culture was exposed to magnetic field of 7 mT, which was 1.1 times higher than the q_P/(q_S ? q_P) value obtained without magnetic exposure. Therefore, the SMF promoted diversion of more acetyl-CoA towards PHB synthesis and could offset adverse effects of high acetate concentration and low temperature. These results provide evidence that SMF enhances PHB production by activated sludge.     

Pb(II) adsorption from aqueous solutions by raw and treated biomass of maize stover – A comparative study

The potential to remove Pb(II) ion from wastewater treatment systems using raw and treated maize stover through adsorption was investigated in batch experiments. To achieve this, batch mode experiments were conducted choosing specific parameters such as pH (2–8), dosage concentration (2–30 g L⁻¹), contact time (5–180 min), temperature (20–45 °C) and metal ion concentrations (10–50 mg L⁻¹). Adsorption was pH-dependent showing a maximum at pH value 5. The equilibrium sorption capacities of raw and treated maize stover were 19.65 and 27.10 mg g⁻¹, respectively. The adsorption data fitted well to the Langmuir isotherm model. Kinetic studies revealed that the adsorption process followed pseudo-second-order model. The calculated thermodynamic parameters showed that the adsorption of Pb(II) was spontaneous and exothermic in nature. Consequently, this study demonstrated that both raw and treated maize stover could be used as adsorbents for the treatment of Pb(II) from industrial wastewaters.     

Performance of a pilot scale up-flow septic tank for on-site decentralized treatment of residential wastewater

The aim of this research was to study the on-site anaerobic treatment of a medium-strength residential wastewater in a pilot-scale up-flow septic tank (UST). The effects of three different hydraulic retention times (HRTs) of 24, 12 and 6 h on the UST performance were investigated. The UST removed 85, 77, and 86% of biochemical oxygen demand (BOD₅), chemical oxygen demand (COD) and total suspended solids (TSS), respectively, at steady state operation and with a 24 h HRT. Decreasing the HRT to 12 and then 6 h resulted in deteriorated effluent quality and significantly reduced reactor performance. The sludge showed a high specific methanogenic activity (SMA) of 15.2 mL CH₄ g^?1 VSS d^?1 with raw wastewater substrate. The solids accumulated in the tank by the end of the experiment had a VSS/TSS of 0.57, demonstrating significant stabilization. Overall, the UST is concluded to be a technically and economically promising alternative to conventional septic tanks for the on-site decentralized treatment of residential wastewater, particularly in the rural communities of developing countries.     

Environmentally friendly hide unhairing: Enzymatic-oxidative unhairing as an alternative to use of lime and sodium sulfide

Various studies have been conducted to develop technologies that minimize the environmental concerns associated with the leather industry. The use of enzymes and oxidizing products during the unhairing step reduces pollution by tanneries as well as process time. In this study, were used an enzymatic extract produced by a strain of Bacillus subtilis – BLBc 11 – and hydrogen peroxide to conduct enzymatic-oxidative unhairing as an alternative to the conventional process (lime and sodium sulfide). Tests for enzymatic-oxidative unhairing were performed by applying crude enzymatic extract at concentrations of 100 U g⁻¹ and 300 U g⁻¹ of hide and hydrogen peroxide at concentrations of 4% and 8%. Tests were conducted comparing the proposed unhairing method, the conventional unhairing and purely enzymatic unhairing, performed with crud enzymatic extract produced by strain BLBc 11. The results showed that the proposed enzymatic-oxidative unhairing method can be used as an alternative to lime and sodium sulfide.     

Achieving stable partial nitritation using endpoint pH control in an SBR treating landfill leachate

The feasibility of using endpoint pH control to achieve stable partial nitritation (PN) in an SBR for landfill leachate treatment was investigated. By imposing a fixed-time anoxia followed by variable-time aeration in an SBR cycle, successful partial nitritation was maintained for 182 days at a nitrogen loading rate of 0.30–0.89 kg/m³/day. The effluent NO₂⁻-N/NH₄⁺-N ratio and the effluent NO₃⁻-N concentration were 1.30 ± 0.22 and 16 ± 9 mg/L, respectively. High free ammonia (FA) and low dissolved oxygen (DO) concentrations were inhibition factors of nitrate formation. The termination of aeration at a suitable endpoint pH was the key to achieve an effluent NO₂⁻-N/NH₄⁺-N ratio close to the stoichiometric value. This endpoint pH control strategy represents practical potentials in the engineered application of combined PN–ANAMMOX processes.     

Sensitivity analysis and optimization for gasoline vapor condensation recovery

Volatile organic compounds (VOCs) are easily evaporated and discharged from everywhere into the atmosphere, especially in various operations of gasoline. The emission of VOCs is always a significant environmental problem, and the control of VOCs pollution has been a hot topic in the field of air purification. In this paper, the condensation separation method for gasoline vapor recovery was investigated and four gasoline vapors of S1–S4 were selected for the sensitivity analysis and optimization of the condensation process, using the Model Analysis Tools from Aspen Plus. Generally, to control VOCs pollution efficiently, both the vapor recovery efficiency and the outlet vapor concentration of the condensation recovery system should be simultaneously considered. Then an optimized three-stage condensation process was proposed, whose condensation temperatures were optimized and designed at 1 °C, −40 °C and −110 °C, respectively. Further, based on the comprehensive consideration of both meeting the more strict VOCs emission standard and ensuring the condensation recovery system work stably and economically, it was recommended that the maximum total vapor recovery efficiencies for S1–S4 should be 99.73%, 99.79%, 99.82% and 99.19%, and the minimum outlet vapor concentrations be 2.87 g/m³, 2.75 g/m³, 3.04 g/m³ and 16.98 g/m³, respectively. Accordingly, the condensation temperature of the copious cooling stage should be set at −130 °C. Moreover, the total cooling duties for the single-stage and three-stage condensation processes were investigated and compared when the condensation temperature of the recovery system ranged from 20 °C to −110 °C. The total cooling duties of the three-stage condensation process for S1–S4 would be saved by 12.23%, 15.68%, 13.96% and 15.65%, respectively. Finally, a three-stage condensation system was developed for the industrial gasoline vapor recovery, which has performed well since its installation.     

Removal of H2S by co-immobilized bacteria and fungi biocatalysts in a bio-trickling filter

Biological control of odor gases has gained more attention in recent years. In this study, removal performance of a vertical bio-trickling filter inoculated with bacteria and fungi was studied. Bacteria and fungi were isolated from activated sludge in a sewage treatment plant. By adopting “three step immobilization method”, the bio-trickling filter could degrade pollutant immediately once hydrogen sulfide (H₂S) passed. The optimal empty bed resident time was 20 s. The optimal elimination capacity was about 60 g H₂S m^?3 h^?1 with removal efficiency of 95%. And the maximum elimination capacity was 170 g H₂S m^?3 h^?1. Pressure drop was ranged between 5 and 15 mm H₂O per bed over the whole operation. Removal efficiency was not affected obviously after terminating nutrient supply. The bio-trickling filter could recover back after shut down H₂S gaseous and liquid supplies simultaneously. Microbial community structure in the bio-trickling filter was not changed significantly.Combining bacteria and fungi would be a better choice for inoculation into a bio-trickling filter because of the quickly degradation of H₂S and rapid recovery under shut-down experiment. This is the first study attempting to combine bacteria and fungi for removal of H₂S in a bio-trickling filter.     

Disintegration of municipal waste activated sludge by simultaneous combination of acid and ultrasonic pretreatment

The individual and simultaneous effects of acid and ultrasonic pretreatment on the disintegration of municipal waste activated sludge (WAS) were investigated based on chemical properties of WAS. In the combination of acid and ultrasonic pretreatment methods (ultrasonic-acid pretreatment), lowering pH accelerated and enhanced the disintegration of waste biological sludge. Therefore, the same disintegration efficiency (obtained by ultrasonic pretreatment alone) was achieved by the combined pretreatment in shorter sonication times. Optimum pretreatment conditions were ultrasonic power density of 1.0 W/mL and pretreatment time of 10 min for ultrasonic pretreatment alone, and ultrasonic power density of 1.0 W/mL, pretreatment time of 10 min and initial sludge pH of 2.0 for the combined pretreatment. Sludge disintegration degrees were about 30% and 40% under these optimized conditions, respectively. Optimum sludge concentration was found to be 1.0% total solid (TS) content for the combined pretreatment. As a result, ultrasonic-acid pretreatment has been determined as a new and effective combined sludge pretreatment method to improve the sludge disintegration.     

Rotating biological contactors for wastewater treatment – A review

Rotating biological contactors (RBCs) for wastewater treatment began in the 1970s. Removal of organic matter has been targeted within organic loading rates of up to 120 g m⁻² d⁻¹ with an optimum at around 15 g m⁻² d⁻¹ for combined BOD and ammonia removal. Full nitrification is achievable under appropriate process conditions with oxidation rates of up to 6 g m⁻² d⁻¹ reported for municipal wastewater. The RBC process has been adapted for denitrification with reported removal rates of up to 14 g m⁻² d⁻¹ with nitrogen rich wastewaters. Different media types can be used to improve organic/nitrogen loading rates through selecting for different bacterial groups. The RBC has been applied with only limited success for enhanced biological phosphorus removal and attained up to 70% total phosphorus removal. Compared to other biofilm processes, RBCs had 35% lower energy costs than trickling filters but higher demand than wetland systems. However, the land footprint for the same treatment is lower than these alternatives. The RBC process has been used for removal of priority pollutants such as pharmaceuticals and personal care products. The RBC system has been shown to eliminate 99% of faecal coliforms and the majority of other wastewater pathogens. Novel RBC reactors include systems for energy generation such as algae, methane production and microbial fuel cells for direct current generation. Issues such as scale up remain challenging for the future application of RBC technology and topics such as phosphorus removal and denitrification still require further research. High volumetric removal rate, solids retention, low footprint, hydraulic residence times are characteristics of RBCs. The RBC is therefore an ideal candidate for hybrid processes for upgrading works maximising efficiency of existing infrastructure and minimising energy consumption for nutrient removal. This review will provide a link between disciplines and discuss recent developments in RBC research and comparison of recent process designs are provided (Section 2). The microbial features of the RBC biofilm are highlighted (Section 3) and topics such as biological nitrogen removal and priority pollutant remediation are discussed (Sections 4 Biological nutrient removal in RBCs, 5 Priority pollutant remediation in RBCs). Developments in kinetics and modelling are highlighted (Section 6) and future research themes are mentioned.     

Use of advance oxidation process to improve the biodegradability of olive oil mill effluents

In this study, recalcitrant total phenol (TPh) and organic matter removal were investigated at olive mill wastewater (OMW) in sequential Coagulation and Fenton system. This study focused on different operational parameters such as pH, H₂O₂, and Fe²⁺ dosages, and [Fe²⁺]/[H₂O₂] ratios. The optimum conditions were determined as; pH = 3; [Fe²⁺] = 2.5 g/L; [Fe²⁺]/[H₂O₂] = 2.5. A higher treatment efficiency was achieved at sequential Coagulation and Fenton system (COD, 65.5%) and TPh, 87.2%), compared to coagulation process (COD, 51.4%; total organic carbon (TOC), 38.6% and total nitrogen (TN) 52.1%). This study demonstrated that the Coagulation and Fenton process has a potential for efficient removal of phenolic pollutants from wastewater.     

Synthesis of CuO nanoparticles through green route using Citrus limon juice and its application as nanosorbent for Cr(VI) remediation: Process optimization with RSM and ANN-GA based model

In present investigation, an attempt has been made for the synthesis of cupric oxide nanoparticles (CuONPs) through a green route by utilizing lemon juice extract as a bioreductant. The synthesized CuONPs were characterized through UV–visible spectroscopy, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The CuONPs were utilized for Cr(VI) removal from water through adsorption method in batch mode at different initial Cr(VI) concentration, pH, temperature and CuONPs dosage. The maximum uptake capacity of CuONPs was found to be 16.63 mg of Cr(VI)/g at pH 4.0. Implementation of response surface methodology (RSM) followed by artificial neural network hybridized with genetic algorithm (ANN-GA) approach has resulted maximum Cr(VI) adsorption of 98.8% under the optimized conditions of initial metal concentration 22.5 mg/L, pH 3.81, CuONPs dose 1.28 g/L and temperature 37.1 °C. Under optimum conditions, adsorption isotherm study was conducted, which showed that the fitness of experimental data was well achieved with Langmuir isotherm model illustrating monolayer pattern of adsorption. Thermodynamic study revealed that the process was spontaneous and endothermic in nature, while adsorption kinetics was best explained by pseudo-second order kinetic model.