Sludge Solution Research Articles

Recovery of phosphate from the supernatant of activated sludge pretreated by microwave irradiation through chemical precipitation.

This paper presents a technology of releasing phosphate from activated sludge by using a combined process of microwave irradiation and anaerobic stirring, followed by phosphate recovery from the resulting supernatant via chemical precipitation without addition of chemicals, except for a pH regulator. A series of experiments was conducted to examine the effects of microwave irradiation time, sludge solution pH, sludge concentration, and anaerobic stirring time on the release of phosphate. The results revealed that all of these parameters had a significant effect on the release of phosphate via the proposed combined process, and the combination of 180s of microwave irradiation and 1h of anaerobic stirring was found to give optimal phosphate release. When the sludge solution was acidized before pretreatment, the phosphate concentration of the supernatant increased rapidly. A 25g/L sludge concentration was found to be optimal for the release of phosphate, beyond this concentration, there was no increase in the phosphate release. Under the optimal conditions of phosphate release (irradiation time, 180s; solution pH, 2; sludge concentration, 25g/L; anaerobic stirring time, 1h), the total orthophosphate (PT) concentration in the supernatant reached 396mg/L, accompanied by high concentrations of metal cations such as Ca, Mg, K, Al, and Fe. When the pH of the supernatant was adjusted to 9-10, the recovery efficiency of phosphate reached approximately 95%. The analysis results indicated that the main components of the collected precipitates were amorphous calcium phosphate and struvite, which can be used as alternate phosphate minerals.

정수장 슬러지 농축조 배출수의 망간 농도에 미치는 pH의 영향

정수공정 중에 응집된 망간은 슬러지 농축조에 체류하는 동안 재용출 되어 배출수의 망간 허용기준치를 초과하는 문제가 발생되고 있다. 본 연구에서는 정수공정 중에 슬러지 농축조 배출수의 pH를 조정함으로써 망간 농도에 미치는 pH의 영향에 대하여 연구하였다. 초기 pH 6.1에서는 응집된 슬러지로부터 망간이 재용출 되어 청정지역 배출 기준인 2mg/L를 초과하였으나 NaOH, KOH, CaO, <TEX>$Ca(OH)_2$</TEX>, <TEX>$CaCO_3$</TEX> 등 알칼리 물질을 이용하여 pH를 상승시켰을 경우 망간 농도를 청정지역 배출 기준 이하로 낮출 수 있었다. 또한 알칼리성 물질로서 석회석 광산에서 선별과정 중 발생하는 폐석회석을 이용하여 정수장 슬러지의 망간 재용출을 억제할 수 있는 가능성을 확인하였다. Manganese in sludge precipitated during water treatment might be soluble again in effluent from sludge thickener. If that happens, the manganese concentration of effluent from water treatment plant will exceed the limit for clean reservation. In this study the influence of pH on Mn concentration of effluent from sludge thickener of water treatment plant was investigated. When the pHs of sludge solutions increased with alkaline materials such as NaOH, KOH, CaO, <TEX>$Ca(OH)_2$</TEX>, <TEX>$CaCO_3$</TEX>, the Mn concentrations of sludge solutions decreased under the limit. The Mn concentration of effluent from sludge thickener could be controlled with waste limestones from beneficiation process at limestone mine as an alkaline material.

Preparation and performance of homogeneous braid reinforced cellulose acetate hollow fiber membranes

Homogeneous braid reinforced (HBR) cellulose acetate (CA) hollow fiber membranes were fabricated through dry–wet spinning process which consisted of CA separation layer and CA hollow tubular braids. The performance of various CA concentration membranes were characterized in terms of pore size distribution, pure water flux (PWF), protein solution flux (PSF), mechanical strength, and membrane morphologies were observed by a scanning electron microscope. The results showed that the HBR CA hollow fiber membranes, especially with high CA concentration in the dope solutions, possessed dense and smooth outer surface. The tensile strength of HBR CA hollow fiber membranes which exceeded 11 MPa mainly depended on the tubular braids. With the increase of CA concentration, the tensile strength and bursting strength of the membranes increased. In addition, there was effective interfacial bonding state between the separation layer and the tubular braid when the CA concentration was higher than 10 wt%. The increase of CA concentration brought about the decrease of membrane pore size and the increase of protein rejection. Considering the PWF, rejection and stable PSF, the best CA concentration in the dope solutions was 10 wt%. Then the membrane fouling and cleaning processes for the activated sludge solution were studied by comparing with reinforced polyvinylidene fluoride (PVDF) hollow fiber membrane. The lower flux decline in the filtration of activated sludge solution and higher recovery in the flux indicated that the HBR CA hollow fiber membrane had better anti-fouling properties than the PVDF membrane.

Effects of dilution ratio and Fe0 dosing on biohydrogen production from dewatered sludge by hydrothermal pretreatment

Biohydrogen fermentation of dewatered sludge (DS) with sewage at ratios from 4:1 to 1:20 was investigated. Hydrothermal pretreatment of the sludge solution was performed to accelerate the organic release from the solid phase. The maximum hydrogen yield of 26.3 ± 0.5 mL H2/g volatile solid (VS) was obtained at a 1:10 ratio. Although addition of zero valent iron (ZVI) to anaerobic system was not new, the study of dosing it to enhance the biohydrogen yield might be the first attempt. While Fe0 plate slightly affected the hydrogen yield, Fe0 powder improved the amount of hydrogen by 16% and shortened the lag time by 36%. The state of bacteria in the reactor added with ZVI powder was changed and the key enzyme activity was improved as well. Correspondingly, the mechanism of ZVI in accelerating the biofermentation process was also proposed. Our research provides a solution for the centralized treatment of DS in a city.

Technique for recovering uranium from sludge-like uranium-bearing wastes using hydrochloric acid

Sludge-like uranium-bearing wastes generated from uranium refining and conversion R&D facilities are stored at the Ningyo-toge Environmental Engineering Center of the Japan Atomic Energy Agency. So far, approximately 1500 t of uranium wastes with radioactivity levels exceeding 10,000 Bq/g have been generated. We have proposed an environmentally benign aqueous process for recovering uranium from wastes using hydrochloric acid (HCl). This makes it possible to dispose of the wastes easily, and to reclaim uranium as a resource. In this process, first, the uranium content in the calcium fluoride (CaF2) sludge along with the entire sludge is dissolved almost completely in aqueous solutions containing HCl and aluminum chloride. The uranium species are then recovered as peroxide from the CaF2 sludge solution. Their characteristics are similar to those specified for uranium ore concentrate. After recovering the uranium content, the uranium concentration in the solution is reduced to below 0.01 mg/L using an iminodiacetic chelating resin. Also, the uranium concentration of the precipitate generated by the neutralization of the barren solution falls below 1 Bq/g.

Study on the interfacial bonding state and fouling phenomena of polyvinylidene fluoride matrix-reinforced hollow fiber membranes during microfiltration

Reinforced polyvinylidene fluoride (PVDF) and polyacrylonitrile (PAN) hollow fiber membranes were prepared through dry–wet spinning process and included PVDF or PAN polymer solutions (coating layer) and matrix PVDF membrane. The performance of the membranes varies with different polymer solutions and is characterized in terms of ink solution and activated sludge flux, dynamic mechanical analysis (DMA), mean pore size, a mechanical strength test, and morphology observations by a scanning electron microscope (SEM). The results of this study indicate that PAN coating layer is easy to peel off from the matrix membrane. Interfacial bonding strength is also detected by dynamic mechanical analysis indirectly. The reinforced membranes show a narrower pore size distribution and smaller mean pore size than the matrix membrane. The elongation at break increases much more and the membranes are endowed with better flexibility performance. The homogeneous-reinforced (HMR) and heterogeneous-reinforced (HTR) membranes have a lower rate of flux decline compared with matrix membrane during ink solution filtration. The main types of all membranes fouling in microfiltration of ink solution were attributed to initial pore blocking followed by cake formation. Then, in the activated sludge solution, the reinforced membranes have stable efficiency in antifouling property for the real MBR system.

Increased power generation from primary sludge by a submersible microbial fuel cell and optimum operational conditions

Microbial fuel cells (MFCs) have received attention as a promising renewable energy technology for waste treatment and energy recovery. We tested a submersible MFC with an innovative design capable of generating a stable voltage of 0.250±0.008V (with a fixed 470Ω resistor) directly from primary sludge. In a polarization test, the maximum power density was 0.18W/m(2) at a current density of 0.8A/m(2) with an external resistor of 300Ω. The anodic solution of the primary sludge needs to be adjusted to a pH 7 for high power generation. The modified primary sludge with an added phosphate buffer prolonged the current generation and increased the power density by 7 and 1.5 times, respectively, in comparison with raw primary sludge. These findings suggest that energy recovery from primary sludge can be maximized using an advanced MFC system with optimum conditions.

Application of forward osmosis on dewatering of high nutrient sludge

A novel approach was designed to simultaneously apply low energy sludge dewatering and nutrient removal for activated sludge using forward osmosis (FO). In this study, the municipal wastewater sludge was spiked with different nutrient concentrations to evaluate FO dewatering performance. The results showed that sludge concentration reached 21,511 and 28,500mg/L after 28h from initial sludge concentration of 3000 and 8000mg/L with flow rate of 150mL/min. Moreover, nutrient and organic compounds in sludge solution were also successfully removed (around 96% of NH4+-N, 98% of PO43--P and 99% of dissolved organic carbon (DOC)) due to steric effect of FO membrane and multi barrier layer of sludge forming on membrane surface. Furthermore, the analysis from Scanning Electron Microscopy & Energy Dispersive X-ray Spectroscopy (SEM–EDS) images recorded that FO membrane was fouled by cake layer of sludge in the active layer and NaCl in the support layer.

Folytonos anyagtovábbítású mikrohullámú kezelőegység fejlesztése

Most branches in the food industry have a considerable wastewater output. The problem is not only the total amount of wastewater production, but also the high content of organic matter. Anaerobic digestion is an effective way of treating wastewater for yielding profitable biogas and alleviating environmental concerns. Pre-treatment of sludge to break down its complex structure can be used for enhancing anaerobic digestibility. Research group of the Department of Process Engineering at the University of Szeged has investigated the applicability and the efficiency of microwave pre-treatment for food industry sludge. The results showed that the microwave treatment of sludge solution resulted in higher biodegradability and enhanced biogas production as well. According to these results a continuous-flow microwave toroidal cavity resonator treating-system was developed.

Effect of ozone pre-treatment on sludge production of aerobic digestion processes

The effect of ozone in a chemical sludge disintegration process was evaluated. Sludge solution chemical oxygen demand (COD), total suspended solids (TSS) and settling were investigated in single and sequential processes. A significant influence of ozone dose on sludge disintegration was observed: ozone was utilised to degrade the soluble organic matter and to destroy cell surfaces and release the cell liquids. For a single ozonation step, we found an optimum ozone dose in the range of 0.008–0.013 g O3/g TSS to give the best COD and TSS removal efficiency. Disintegrated sludge was treated in a sequential process consisting of consecutive ozonation and bio-aeration (i.e. O3 + biological treatment). The tendency was dependent on accumulated ozone, treatment time and operational conditions. An accumulated ozone dose of 0.055 g O3/g TSS in two separate ozonation processes followed by biological treatments led to COD and TSS removal efficiency of 53 and 46.6%, respectively. The removal efficiency was improved by increasing aerobic treatment time and/or by mixing ozonated sludge with non-ozonated sludge. The settling ability of sludge was found to be fast at very low specific ozone doses. An observed tendency was the effect of ozone on cell disintegration and protein liberation. The use of sequential processes improved the settling tendency of sludge.

Comparison and Analysis of Denitrification Effect and Kinetics Regarding Several New Type Carbon Sources

Three typical external carbon sources (i.e. leachate, hydrolysates from primary sludge and starch solution) with regard to the denitrification process were investigated respectively in sequencing batch reactors (SBR) and their denitrification properties were compared to provide the optimum substrate suited for nitrogen removal processes. The variations of nitrogen were examined and nitrate utility ratio as well as carbon consumption rate was exhibited, denitrification kinetics regarding leachate was also analyzed by use of zero-order kinetic model. The experimental results indicated that the similar denitrification trend was achieved between hydrolysates from primary sludge and starch solution other than leachate as carbon source in denitrification system. The nitrate was not entirely degraded and the nitrite generated permanent accumulation. Compared with other carbon sources, leachate in steady operation showed the highest nitrate removal concentration and rate in phase I with an average of 13 mg/L and 86%, respectively. In phase II, the maximum nitrate and carbon decomposition rates were 0.088 g N/g VSS•d and 0.848 g TOC/g VSS•d respectively occurring at leachate as substrate. Thus, stable leachate was considered as the most suitable carbon source in comparison with other substrates.

Enhancing the hydrophilic and antifouling properties of polypropylene nonwoven fabric membranes by the grafting of poly(N-vinyl-2-pyrrolidone) via the ATRP method

In this work, the surface characteristics of poly(N-vinyl-2-pyrrolidone) (PNVP)-modified nonwoven fabric (NWF) membranes and the effects of the surface characteristics on the membranes antifouling properties were investigated. Effects of grafting time, grafting temperature, and monomer concentration on the grafting degree of PNVP were systematically investigated. The effect of grafting degree on the surface characteristics was also investigated. Scanning electron microscopy (SEM) was used to characterize the structural and morphological changes on the membrane surface. The water contact angles decreased from 113±1.2° to 52±3°, which means that the hydrophilicity of the modified NWF was enhanced with increasing PNVP grafting degree. The surface free energy was calculated, which showed an increase after modification. Static bovine serum albumin (BSA) adsorption experiments were carried out, which showed a decrease of 82.5%. Permeation experiments of water and supernatant solution of active sludge were carried out to determine the antifouling characteristics against the extracellular polymeric substance. Results demonstrated that the modified NWF had higher permeation fluxes and lower flux loss in comparison with the original NWF. Bacterial adhesion on the membrane surface was largely suppressed after the introduction of PNVP.

Highly effective antifouling performance of N-vinyl-2-pyrrolidone modified polypropylene non-woven fabric membranes by ATRP method

In this paper, a hydrophilic polymer, poly(N-vinyl-2-pyrrolidone) (PNVP), was grafted on the surface of polypropylene non-woven fabric (PP-NWF) membrane via ozone surface activation and surface-initiated atom transfer radical polymerization (ATRP). The grafting degree of PNVP on the membrane surface can be modulated in a wide range through the variation of grafting time. Chemical and morphological changes of the PNVP-modified membrane surface were characterized in detail by Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence spectroscopy and scanning electron microscopy (SEM). The hydrophilicity of the membrane increased upon modification with the water contact angle decreasing from 113.0 ± 1.2° to 52.1 ± 3°. Permeation experiments of water and supernatant solution of active sludge were conducted to evaluate the antifouling property of the PNVP-modified membranes, which results indicated that the modified membranes had higher permeation fluxes with enhanced rejection rates, lower flux loss and better antifouling property than those of the original NWF membrane. Bacterial adhesion on the studied membrane surfaces was also investigated, which showed that bacteria were restrained from growing on PNVP-modified membranes, and adhesion of bacteria was reversible due to the enhanced hydrophilicity.

Application of acidic thermal treatment for one- and two-stage anaerobic digestion of sewage sludge

The effectiveness of acidic thermal treatment (ATT) was examined in a 106-day continuous experiment, when applied to one- or two-stage anaerobic digestion of sewage sludge (4.3% TS). The ATT was performed at 170 °C and pH 5 for 1 hour (sulfuric acid for lowering pH). The one-stage process was mesophilic at 20 days hydraulic retention time (HRT), and incorporated the ATT as pre-treatment. The two-stage process consisted of a thermophilic digester at 5 days HRT and a mesophilic digester at 15 days HRT, and incorporated the ATT as interstage-treatment. On average, VSS reduction was 48.7% for the one-stage control, 65.8% for the one-stage ATT, 52.7% for the two-stage control and 67.6% for the two-stage ATT. Therefore, VSS reduction was increased by 15-17%, when the ATT was combined in both one- and two-stage processes. In addition, the dewaterability of digested sludge was remarkably improved, and phosphate release was enhanced. On the other hand, total methane production did not differ significantly, and color generation was noted in the digested sludge solutions with the ATT. In conclusion, the anaerobic digestion with ATT can be an attractive alternative for sludge reduction, handling, and phosphorus recovery.

Hydrophilic and antibacterial properties of polyvinyl alcohol/4-vinylpyridine graft polymer modified polypropylene non-woven fabric membranes

Membrane filtration processes in water treatment have increased considerably in the past decades. However, the disadvantages of common hydrophobic membrane materials are that they cause serious bio-fouling and decrease of permeate fluxes. In this work, a novel polyvinyl alcohol/4-vinylpyridine graft polymer (PVA-g-4VP) was prepared and adsorbed on polypropylene non-woven fabric (NWF) membrane surface and pore walls to improve both hydrophilic and antibacterial properties of the membrane. Fourier transform infrared spectroscopy and elemental analysis were employed to confirm the graft reaction. X-ray photoelectron spectroscopy and environmental scanning electron microscopy were employed to confirm the modification on the membranes. Water contact angle was measured to evaluate the hydrophilicity. The water contact angles for the membranes decreased from 123 ± 1.2° to 33.4 ± 2.5° with increasing PVA-g-4VP concentration from 0 to 1.5 wt.% in the adsorption solution during modification. Flux and rejection of the modified membrane in supernatant solution of active sludge were measured. The modified membranes had lower water permeate fluxes, higher rejection rates and better antifouling property than those of the original NWF membrane. Live/dead cell staining results of the attached bacteria on the membranes also revealed that a more antibacterial surface can be obtained by quaternizing PVA-g-4VP modified membrane surface with benzyl bromide.

Disintegration of sewage sludge with bifrequency ultrasonic treatment

A bifrequency ultrasonic generating trough was used to improve disintegration of sewage sludge from thickener tanks. Ultrasonic operating parameters such as frequency, power, and time were optimized. Ultrasonic treatment successfully disintegrated the floc structure of sewage sludge and promoted the release of organic matter and metal ions such as Ca2+ and Mg2+. After ultrasonic treatment, soluble chemical oxygen demand (SCOD) in the sludge solution increased 11.28-49.06%, while the concentrations of Ca2+ and Mg2+ rose 5.5-25.0% and 2.7-19.0%, respectively. The ultrasonic frequency of 25 kHz was most effective in disintegrating sludge, and high energy densities and longer treatment time increased SCOD and metal ion release. The optimal parameters that promoted the increase SCOD were 25 kHz, 75 W/L and 60 s. Under these conditions, double-frequency ultrasonication was more effective than single-frequency ultrasonication.

Effect of process parameters on the energy requirement in ultrasonical treatment of waste sludge

Mechanical treatment methods are used as pre-treatment methods in order to enhance the efficiency of conventional sludge treatment processes and the sludge becomes more suitable for its complete treatment. The ultrasound is an alternative method among other methods, but because of its high energy requirement it should be optimized before utilization. This work gives the optimized parameters such as sonication time, sonication power (these parameters are the two factors which play part for energy calculations), type of sludge, cooling requirements and solid content in the sludge solution. Even if the previous researchers prefer to use the energy (specific energy usually), we have found out that both the sonication time and the sonication power have individual importance. For municipal sludge the main conclusion can be summarized as: “high power-short retention time” is more effective than “low power-long retention time”. As this phenomenon may alter from sludge to sludge, various combinations of power and retention time should be tried while keeping the volume small and the concentration below a certain level. The process should be performed at moderate temperatures and the efficiency increases if the sludge is as homogeneous as possible.

Effect of thermochemical sludge pretreatment on sludge reduction and on performances of anoxic‐aerobic membrane bioreactor treating low strength domestic wastewater

AbstractBACKGROUND: Reduction of excess sludge production has become an urgent issue. An investigation into the influence of thermochemical sludge pretreatment on sludge reduction in a bench‐scale anoxic‐aerobic membrane bioreactor was performed. Two systems were operated. In one system, part of the mixed liquid (1.5% of the influent flow rate) was pretreated thermochemically (at 80 °C, pH 11 and 3 h) and returned to the bioreactor. This study examined and evaluated the effect of thermochemical sludge pretreatment on the reduction of excess sludge and on the performance of the system.RESULTS: The average solubilization efficiency of the pretreated sludge was found to be about 0.2. The sludge production rate of the experimental system (E‐MBR) was less than that of the control (C‐MBR) by about 33%. The total phosphorus was removed mainly by normal cell synthesis, with removal efficiencies of 38–40% and 40–42% for the E‐MBR and C‐MBR, respectively. The total nitrogen removal in the E‐MBR was slightly higher than in the C‐MBR due to supply of soluble chemical oxygen demand (SCOD) from the digested sludge solution as an external carbon source. The mixed liquor volatile suspended solids (MLVSS) and mixed liquor suspended solids (MLSS) ratios for the two systems were almost identical, in the range 74–77%, indicating that the inorganics from the disintegrated cells do not accumulate as particulates in the reactor. The TMP was maintained at less than 6 cmHg for 180 days without membrane cleaning.CONCLUSION: Thermochemical sludge pretreatment can play an important role in reducing sludge production. The qualities of the effluent water were not significantly affected during 6 months of operation. Copyright © 2009 Society of Chemical Industry

Metallic lead recovery from lead-acid battery paste by urea acetate dissolution and cementation on iron

A suitable hydrometallurgical and environmentally friendly process was studied to replace the currently used practices for recycling lead-acid batteries via smelting. Metallic lead was recovered by cementation from industrial lead sludge solutions of urea acetate (200 to 500 g/L) using different types of metallic iron substrates (nails, shaving or powder) as reducing agents. Under specific operating conditions, up to 99.7% of lead acid battery paste, mainly composed of PbSO 4, PbO 2 and PbO·PbSO 4 species, was converted to metallic lead.. The conversion of the metallic lead and rate of the cementation reaction were strictly dependent on the type of iron substrate used as the reductant and the best operating conditions were found with iron powder. The rate constant of the lead recovery reaction under these conditions was 3 · 10 − 3 1/s and the rate determining process was the diffusion controlled cathodic reaction (E a = 1.9 kJ/mol). The reaction residues and the recovered lead were characterized by XRD analysis. Metallic lead morphology and purity were studied by SEM and EDS respectively. Addition of proper amounts of concentrated sulphuric acid to the exhausted cementation solution led to the quantitative recovery of iron(II) by crystallization of (NH 4) 2SO 4FeSO 4 .6H 2O.

Membrane fouling and process performance of forward osmosis membranes on activated sludge

An innovative osmotic membrane bioreactor (OMBR) is currently under development, based on forward osmosis (FO) driven by an osmotic pressure difference. For the OMBR to be both technically and economically viable, the performance of the FO membranes has to be sufficiently high, while membrane fouling and draw solution leakage has to be low. The effect of temperature, membrane type, membrane orientation, type and concentration of draw solution was investigated to optimize FO membrane performance using deionised water. Membrane fouling and draw solution leakage was investigated in this work by laboratory scale FO experiments using an activated sludge solution from a membrane bioreactor (MBR). The best FO performance with an activated sludge solution was found with a FO-type membrane ( J = 6.2 l/m 2 h at 20 ± 2 °C with 0.5 M NaCl corresponding to π = 24 bar). Draw solutions from salts consisting of monovalent ions (NaCl and NaNO 3) performed better than salts consisting of bivalent ions (MgSO 4 and ZnSO 4), while the flux of the FO membrane were non-linearly related to the concentration of the draw solution. Internal concentration polarization did hamper the FO performance as a result of the thickness and structure of the porous substructure of the investigated membranes. Both reversible and irreversible membrane fouling were not found during the FO experiments using activated sludge solutions. Furthermore no substantial draw solution leakage was found for the FO membranes at various draw solution concentrations for different draw solutions.