The kinetic behaviors of simultaneous phosphorus release and denitrification on sludge for BNR processes

Abstract

In this study, we investigated the kinetic behaviors of phosphorus release and denitrification on sludge for two biological nutrient removal (BNR) processes, i.e., suspension growth process (A₂O) and combined suspension‐biofilm growth process (TNCU) under anoxic condition. The readily biodegradable substrate and nitrate loadings, 20–180 mg HAc‐COD/g MLSS and 4–25 mg NO₃‐N/g MLSS respectively, are controlled in a batch reactor for phosphorus release and denitrification of sludge taken from A₂O and TNCU processes under various SRT (5, 10 and 15 days) operating conditions. Experimental results indicated that the occurrence of simultaneous phosphorus release and denitrification is a kinetic competition mode under anoxic condition in the presence of a readily biodegradable substrate. Moreover, the available substrate in bulk solution determined the kinetic behaviors of phosphorus release and denitrification. To prevent nitrate inhibition, the sludge is exposed to a C/N ratio higher than 6.1 for phosphorus release. The sludge's phosphorus content (as created by different SRT processes) and initial nitrate loading dominated the kinetics of phosphorus release and denitrification, respectivley. Moreover, the sludge of suspension gorwth process demonstrated a higher phosphorus release potential than the combined suspension‐biofilm growth process. However, the nitrate inhibition is significant for A₂O sludge also. Based on proposed phosphorus release rate equation, the rate constant would be reduced by denitrification about 31–67% and 20–45% for A₂O and TNCU processes, respectively.     

Biological hydrogen production from sterilized sewage sludge by anaerobic self-fermentation

Due to richness in proteins and carbohydrates, the sewage sludge produced from the wastewater treatment processes is becoming a potential substrate for biological hydrogen production. In this study, sterilized sludge was employed to produce hydrogen by batch anaerobic self-fermentation without any extra-feeds and extra-seeds. Sterilization can screen hydrogen-producing microorganisms from sludge microflora and release organic materials from microbial cells of sludge. Experimental results suggested that sterilization could accelerate and increase the hydrogen production of sewage sludge in the anaerobic self-fermentation, and the biogas did not contain methane. The hydrogen yield was increased from 0.35 mL H₂/g VS (raw sludge) to 16.26 mL H₂/g VS (sterilized sludge). Although sterilization could fully inhibit the activity of methanogens in the sludge, the hydrogen consumption still occurred in the anaerobic self-fermentation of sterilized sludge due to the existence of other hydrogen-consuming actions. The decrease of pH in the anaerobic self-fermentation of sterilized sludge was very lower (from 6.81 to 6.56) because NH₄⁺ produced by degradation of proteins could neutralize organic acids produced in the process. The soluble chemical oxygen demand (SCOD) increase of sterilized sludge was higher than that of raw sludge. Volatile fatty acids (VFA) were the important by-products and acetate was the major composition. The hydrogen fermentation of carbohydrates was the major source of hydrogen production.     

Sludge reduction potential of the activated sludge process by integrating an oligochaete reactor

An oligochaete reactor linked to an integrated oxidation ditch with vertical cycle (IODVC) was used to investigate the sludge reduction potential induced by worms. The presence of Tubificidae was observed in the worm reactor throughout the operational period after its inoculation, and Tubificidae was occasionally found in the IODVC. Free-swimming worms, Aeolosoma hemprichi, Nais elinguis, and Aulophorus furcatus, were found in both the IODVC and the worm reactor, but A. hemprichi was dominant. A. hemprichi reached its maximum, 322 and 339 Aeolosoma/mL mixed liquor on day 49 in the worm reactor and the IODVC, respectively. The presence of oligochaetes or the integration of worm reactor with the IODVC had little effect on sludge yield, but the worm growth was helpful for improving sludge settling characteristics. The average sludge yield and sludge volume index (SVI) in the IODVC were 0.33 kgSS/kgCOD(removed) and 78 mL/g, respectively. The worm presence had little impact on effluent quality of the IODVC, but it caused phosphorus release into the effluent. The average COD, NH(4)(+)-N, and SS concentrations in the effluent of the IODVC were 49.06, 12.82, and 58.25 mg/L, respectively. No total nitrogen (TN) release into the effluent of the IODVC occurred.     

Digestion of thermally hydrolyzed sewage sludge by anaerobic sequencing batch reactor

Laboratory experiments were conducted to investigate the performance of an anaerobic sequencing batch reactor (ASBR) for the digestion of thermally hydrolyzed sewage sludge. Both mesophilic ASBR and continuous-flow stirred tank reactors (CSTR) were evaluated with an equivalent loading rate of 2.71 kg COD/m(3)day at 20-day hydraulic retention time (HRT) and 5.42 kg COD/m(3)day at 10-day HRT. The average total chemical oxygen demand (TCOD) removals of the ASBR at the 20-day and 10-day HRT were 67.71% and 61.66%, respectively. These were 12.38% and 27.92% higher than those obtained by CSTR. As a result, the average daily gas production of ASBR was 15% higher than that of the CSTR at 20-day HRT, and 31% higher than that of the CSTR at 10-day HRT. Solids in thermally hydrolyzed sludge accumulated within ASBR were able to reach a high steady state with solid content of 65-80 g/L. This resulted in a relatively high solid retention time (SRT) of 34-40 days in the ASBR at 10-day HRT. However, too much solid accumulation resulted in the unsteadiness of the ASBR, making regular discharge of digested sludge from the bottom of the ASBR necessary to keep the reactor stable. The evolution of the gas production, soluble chemical oxygen demand (SCOD) and volatile fatty acids (VFAs) in an operation cycle of ASBR also showed that the ASBR was steady and feasible for the treatment of thermally hydrolyzed sludge.     

Morphological study of the granules in UASB and hybrid reactors

Morphology of the granules formed in anaerobic digestion of distillery wastewater was studied in two laboratory scale bioreactors i.e., upflow anaerobic sludge blanket reactor and hybrid reactor. The effects of two different inoculum sludges in early granulation and start-up were studied. Study revealed that earlier start-up and granulation of biomass could be achieved using mixed sludge (anaerobic digested sludge: cowdung and aerobic sludge) than anaerobically digested sludge. Scanning electron microscope (SEM) study of the granules showed predominance of Methanosarcina and Methanothrix type of species on the surface of granules. The change in the morphology and other physical parameters of the granules due to increase in organic loading rate were also studied. The size distribution of granules across the height of the sludge bed showed that the granules of larger diameter having higher settling velocity are mainly concentrated at the lower active zones while smaller sized granules having less settling velocity were found at the top and middle zones of the sludge bed.     

Isostructural and Multivalent Anion Substitution toward Improved Phosphate Cathode Materials for Sodium‐Ion Batteries

Polyanion‐type phosphate materials are highly promising cathode candidates for next‐generation batteries due to their excellent structural stability during cycling; however, their poor conductivity has impeded their development. Isostructural and multivalent anion substitution combined with carbon coating is proposed to greatly improve the electrochemical properties of phosphate cathode in sodium‐ion batteries (SIBs). Specifically, multivalent tetrahedral SiO₄^4? substitute for PO₄^3? in Na₃V₂(PO₄)₃ (NVP) lattice, preparing the optimal Na_3.1V₂(PO₄)_2.9(SiO₄)_0.1 with high‐rate capability (delivering a high capacity of 82.5 mAh g^?1 even at 20 C) and outstanding cyclic stability (≈98% capacity retention after 500 cycles at 1 C). Theoretical calculation and experimental analyses reveal that the anion‐substituted Na_3.1V₂(PO₄)_2.9(SiO₄)_0.1 reduces the bandgap of NVP lattice and enhanced its structural stability, Na⁺‐diffusion kinetics and electronic conductivity. This strategy of multivalent and isostructural anion substitution chemistry provides a new insight to develop advanced phosphate cathodes.     

Preparation and characterization of gold doped (Zn,Cd)S mixed phosphors for mechano-optical transducers

When mechanically excited, initially the ML intensity increases, attains a maximum value and then decreases with time. The total ML intensityI _T initially increases with the impact velocityV _o of piston and attains a saturation value for higher values ofV _o and follows the relationI _T=I _T ^o exp(−V _c/V _o) whereI _T ^o andV _c are constants. The ML intensity is maximum for 20% CdS contents in the (Zn, Cd)S phosphors due to increase in hardness which may in turn increase the fracture stress and subsequently the piezoelectric field strength. The wavelength corresponding to the peak of both the ML and PL spectra shift towards longer wavelength with increasing CdS contents. Some models are discussed and it is concluded that the impulsive deformation of these phosphors may be due to piezoelectrification of newly created surfaces. The similarity of ML spectra with EL and PL spectra suggests that although the excitation processes are different, emission process is governed by the states of similar nature.     

Inhibition of sulfate reduction by iron, cadmium and sulfide in granular sludge

This study investigated the inhibition effect of iron, cadmium and sulfide on the substrate utilization rate of sulfate reducing granular sludge. A series of batch experiments in a UASB reactor were conducted with different concentrations of iron (Fe²⁺, 4.0–8.5 mM), cadmium (Cd²⁺, 0.53–3.0 mM) and sulfide (4.2–10.6 mM), the reactor was fed with ethanol at 1 g chemical oxygen demand (COD)/L and sulfate to yield a COD/SO₄²⁻ (g/g) ratio of 0.5. The addition of iron, up to a concentration of 8.1 mM, had a positive effect on the substrate utilization rate which increased 40% compared to the rate obtained without metal addition (0.25 g COD/g VSS-d). Nonetheless, iron concentration of 8.5 mM inhibited the specific substrate utilization rate by 57% compared to the substrate utilization rate obtained in the batch amended with 4.0 mM Fe²⁺ (0.44 g COD/g VSS-d). Cadmium had a negative effect on the specific substrate utilization rate at the concentrations tested; at 3.0 mM Cd²⁺ the substrate utilization rate was inhibited by 44% compared with the substrate utilization rate without metal addition. Cadmium precipitation with sulfide did not decrease the inhibition of cadmium on sulfate reduction. These results could have important practical implications mainly when considering the application of the sulfate reducing process to treat effluents with high concentrations of sulfate and dissolved metals such as iron and cadmium.     

Reduction of excess sludge production in sequencing batch reactor through incorporation of chlorine dioxide oxidation

In this study, chlorine dioxide (ClO₂) instead of chlorine (Cl₂) was proposed to minimize the formation of chlorine-based by-products and was incorporated into a sequencing batch reactor (SBR) for excess sludge reduction. The results showed that the sludge disintegrability of ClO₂ was excellent. The waste activated sludge at an initial concentration of 15 g MLSS/L was rapidly reduced by 36% using ClO₂ doses of 10 mg ClO₂/g dry sludge which was much lower than that obtained using Cl₂ based on similar sludge reduction efficiency. Maximum sludge disintegration was achieved at 10 mg ClO₂/g dry sludge for 40 min. ClO₂ oxidation can be successfully incorporated into a SBR for excess sludge reduction without significantly harming the bioreactor performance. The incorporation of ClO₂ oxidation resulted in a 58% reduction in excess sludge production, and the quality of the effluent was not significantly affected.     

Anaerobic biogranulation in a hybrid reactor treating phenolic waste

Granulation was examined in four similar anaerobic hybrid reactors 15.5L volume (with an effective volume of 13.5L) during the treatment of synthetic coal wastewater at the mesophilic temperature of 27+/-5 degrees C. The hybrid reactors are a combination of UASB unit at the lower part and an anaerobic filter at the upper end. Synthetic wastewater with an average chemical oxygen demand (COD) of 2,240 mg/L, phenolics concentration of 752 mg/L and a mixture of volatile fatty acids was fed to three hybrid reactors. The fourth reactor, control system, was fed with a wastewater containing sodium acetate and mineral nutrients. Coal waste water contained phenol (490 mg/L); m-, o-, p-cresols (123.0, 58.6, 42 mg/L); 2,4-, 2,5-, 3,4- and 3,5-dimethyl phenols (6.3, 6.3, 4.4 and 21.3mg/L) as major phenolic compounds. A mixture of anaerobic digester sludge and partially granulated sludge (3:1) were used as seed materials for the start up of the reactors. Granules were observed after 45 days of operation of the systems. The granules ranged from 0.4 to 1.2 mm in diameter with good settling characteristics with an SVI of 12 mL/gSS. After granulation, the hybrid reactor performed steadily with phenolics and COD removal efficiencies of 93% and 88%, respectively at volumetric loading rate of 2.24 g COD/Ld and hydraulic retention time of 24 h. The removal efficiencies for phenol and m/p-cresols reached 92% and 93% (corresponding to 450.8 and 153 mg/L), while o-cresol was degraded to 88% (corresponding to 51.04 mg/L). Dimethyl phenols could be removed completely at all the organic loadings and did not contribute much to the residual organics. Biodegradation of o-cresol was obtained in the hybrid-UASB reactors.     

Pilot-scale treatment of a trichloethylene rich synthetic wastewater in anaerobic hybrid reactor,with morphological study of the sludge granules

A pilot-scale research was conducted to study the biodegradation of trichloroethylene (TCE) in anaerobic hybrid reactor (AHR). At an influent TCE and COD concentrations of 50 and 2,000 mg/l, respectively, the AHR showed a maximum 99.93 ± 0.13 and 97.81 ± 0.42 % of TCE and COD removals, respectively, at 24 h of hydraulic retention time. The flocculent sludge (<0.5 mm diameter in size) was gradually converted to compact granular sludge (>2 mm diameter in size) after the completion of the acclimatization study. The biomass growth yield, the maximum substrate (COD), and the maximum co-substrate (TCE) utilization rates were found to be 0.05 mg VSS/mg COD/day, 0.526 mg COD/mg VSS/day, and 0.0125 mg TCE/mg VSS/day, respectively. The AHR has the high potentiality for the treatment of high concentration of TCE present in some industrial wastewater.     

Nitrate-dependent biodegradation of quinoline,isoquinoline, and 2-methylquinoline by acclimated activated sludge

The anaerobic degradation of quinoline, isoquinoline and 2-methylquinoline was investigated under nitrate-reducing conditions with acclimated activated sludge. Quinoline was completely transformed during degradation with an optimum COD/NO₃–N ratio of 7. Isoquinoline and 2-methylquinoline were also completely transformed; however, nitrate consumption was much lower with the optimum COD/NO₃–N ratios being in the ranges of 83–92 and 21–26, respectively. GC-MS analyses showed that during degradation, quinoline and isoquinoline were transformed by hydroxylation into 2(1H)-quinolinone and 1(2H)-isoquinolinone, respectively. While quinoline was completely mineralized, only 92% of isoquinoline was mineralized, and 1(2H)-isoquinolinone remained in the effluent. 2-Methylquinoline was transformed by hydrogenation to 1,2,3,4-tetrahydro-2-methyl-quinoline, and further degradation resulted in cleavage of the heterocyclic ring leaving 4-ethyl-benzenamine. Both the metabolites remained in the effluent, resulting in the low mineralization of 2-methylquinoline (58%). This is the first time that 2-methylquinoline is observed degradable under denitrifying conditions, and its metabolites are identified.     

COD, para-chlorophenol and toxicity removal from para-chlorophenol containing synthetic wastewater in an activated sludge unit

Chlorinated phenolic compounds present in some chemical industry wastewaters cause severe toxic effects on the organisms and often are resistant to biological degradation. Synthetic wastewater containing different concentrations of para-chlorophenol (4-chlorophenol, 4-CP) was biologically treated in an activated sludge unit for COD, 4-CP and toxicity removal. Effects of feed 4-CP concentration on COD, 4-CP, toxicity removals and on sludge volume index were investigated at a constant sludge age of 20 days and hydraulic residence time (HRT) of 25 h. Resazurin method based on dehydrogenase activity was used for determination of the toxicity of the feed and effluent wastewater. COD and 4-CP removals were not affected by the presence of 4-CP in the wastewater up to feed 4-CP concentration of 925 mg l(-1) because of almost complete degradation of 4-CP yielding lower than 50 mg l(-1) 4-CP in the aeration tank. Percent COD, 4-CP and toxicity removals decreased and the effluent COD, 4-CP and toxicity levels increased with further increases in the feed 4-CP concentrations above 925 mg l(-1) because of inhibitory concentrations of 4-CP in the reactor. Biomass concentration in the aeration tank decreased and the sludge volume index (SVI) increased with feed 4-CP concentrations above 925 mg l(-1) resulting in lower COD and 4-CP removal rates. The rates of COD and 4-CP removals indicated substrate (4-CP) inhibition for the feed 4-CP concentrations above 925 mg l(-1) corresponding to the reactor 4-CP of above 200 mg l(-1). The system should be operated at the feed 4-CP concentrations of less than 900 mg l(-1) (4-CP(R) < 200 mg l(-1)) in order to obtain high rates and extents of COD, 4-CP and toxicity removals at a sludge age of 20 days and HRT of 25 h.     

Adsorption of heavy metals from wastewater with waste activated sludge

Abstract

The purpose of this study is the investigation of the adsorption of heavy metals from wastewater with waste activated sludge (WAS) so as to increase the operational flexibility of activated sludge processes for the shock loading problems of heavy metals. By contacting the raw wastewater with WAS, before it entered the activated sludge process unit, some heavy metals in the wastewater were removed, and the pH value of the acidic wastewater rose. Five metals, Cu, Zn, Ni, Cd and Pb, were studied, some factors which affected this biosorption phenomena were investigated, and expressions of the adsorption isotherms were discussed. A semi‐empirical mass transfer‐adsorption model was developed to describe the kinetic experimental data.     

双频超声破解污泥实验方法

使用20kHz和25kHz双频超声破解污泥装置,根据污泥滤液COD、NH3-N、TP的增量研究复频超声破解污泥的效果,并且详细探讨了影响复频超声破解污泥的影响因素（不同频率组合、不同作用方式、不同功率组合、不同时间组合）。实验结果表明双频超声更有利于污泥破解,为污泥破解方法的应用和今后进一步扩大其研究提供一定的基础。     

Realizing Over 13% Efficiency in Green‐Solvent‐Processed Nonfullerene Organic Solar Cells Enabled by 1,3,4‐Thiadiazole‐Based Wide‐Bandgap Copolymers

Two novel wide‐bandgap copolymers, PBDT‐TDZ and PBDTS‐TDZ, are developed based on 1,3,4‐thiadiazole (TDZ) and benzo[1,2‐b:4,5‐b′]dithiophene (BDT) building blocks. These copolymers exhibit wide bandgaps over 2.07 eV and low‐lying highest occupied molecular orbital (HOMO) levels below −5.35 eV, which match well with the typical low‐bandgap acceptor of ITIC, resulting in a good complementary absorption from 300 to 900 nm and a low HOMO level offset (≤0.13 eV). Compared to PBDT‐TDZ, PBDTS‐TDZ with alkylthio side chains exhibits the stronger optical absorption, lower‐lying HOMO level, and higher crystallinity. By using a single green solvent of o‐xylene, PBDTS‐TDZ:ITIC devices exhibit a large open‐circuit voltage (V_oc) up to 1.10 eV and an extremely low energy loss (E_loss) of 0.48 eV. At the same time, the desirable high short‐circuit current density (J_sc) of 17.78 mA cm⁻² and fill factor of 65.4% are also obtained, giving rise to a high power conversion efficiency (PCE) of 12.80% without any additive and post‐treatment. When adopting a homotandem device architecture, the PCE is further improved to 13.35% (certified as 13.19%) with a much larger V_oc of 2.13 V, which is the best value for any type of homotandem organic solar cells reported so far.     

Synthesis and characterization of catalysts produced from paper mill sludge: I. Determination of NOx removal capability

Characteristics and catalytic properties of a series of carbon-based catalysts (CBCs) produced from paper mill sludge were evaluated. The major processes involved in the production of the catalysts were chemical activation, impregnation, pyrolysis, and post pyrolysis rinsing. The porous structure, catalytic activity and thermostability of the catalysts were tailored during the production stage by introducing hetero-atoms (zinc chloride, and ferric nitrate) in the carbon structure. Characterization of the produced CBCs included determination of the surface area, pore size, and pore size distribution (PSD) from standard N₂-adsorption isotherm data. The extent of graphitization and the presence of metal crystals were identified from X-ray diffraction (XRD). The limit of the catalyst gasification was estimated from thermogravimetric analysis (TGA) conducted in an oxidized environment. The NO_x reduction capability of the produced catalysts was evaluated in the presence of carbon monoxide using a fixed bed reactor. The reaction temperature ranged from 300 to 500°C. It was shown that paper mill sludge is an excellent precursor for the production of CBCs with NO_x removal capability of 66–94%. The catalytic capability of the produced CBCs varied according to the method of production, catalyst surface properties (surface area, pore structure, PSD), metal composition and reaction temperature. The highest NO_x removal capacity was observed for the catalytic reactions carried out at 400°C. The mesoporous catalyst produced with a Zn:Fe molar ratio of 1:0.5 exhibited the maximum NO_x removal catalytic activity of 94%.     

Studies on land application of sewage sludge and its limiting factors

Field experiments were conducted to study the effect of sewage sludge application on the heavy metal content in soils and grasses. The sewage sludge was obtained from Northern Shenyang Wastewater Treatment Plant, China, and applied at 0, 15, 30, 60, 120 and 150 t ha⁻¹. Native grasses Zoysia japonica and Poa annua were chosen as experimental plants. The experimental results showed that nutrient content of the soil, especially organic matter, was increased after sewage sludge application. The grass biomass was increased and the grass growing season was longer. Heavy metal concentrations in the soil also increased; however, the Zn content did not exceed the stringent Chinese environmental quality standard for soil. Pb and Cu did not exceed the standard for B grade soil, but Cd concentration in soil amended by sewage sludge has exceeded the B grade standard. Therefore, it is suggested that the sewage sludge produced from the wastewater treatment plant should not be applied to farmland, for which B grade soil or better is required. The sludge is suitable for application to forestry and grasslands or nurseries where food chain contamination with cadmium is not a concern.     

A theory-based method for correlation and prediction of dense-fluid transport properties

Dense-fluid transport property data for a wide range of compounds have been successfully correlated on the basis of universal curves for the reduced diffusion coefficient,D ^*, the reduced viscosity, η^* and the reduced thermal conductivity, λ^*, against the reduced volumeV/V _o , whereV is the molar volume, andV _o is a characteristic volume equal to the volume of close packing for a system of hard spheres. The reduced transport properties,X ^*, are defined in terms of the low-density hard-sphere values by (X/X _o )(V/V _o )^2–3, whereX is ν, λ, or the product of the number density and the diffusion coefficient. To provide a theoretical justification for this approach, extensive computer simulation results for these transport properties, given in the literature for a system of Lennard-Jones (12–6) molecules, have been considered. It is found that the reduced transport properties for different temperatures are superimposable upon the results for any reference isotherm when plotted versus logV, as found previously for real fluids. However, to reproduce this density dependence at any given temperature on the basis of the universal curves, the characteristic volume for self-diffusion must be greater than that for viscosity or thermal conductivity. Invited paper presented at the Fourth Asian Thermophysical Properties Conference, September 5–8, 1995, Tokyo, Japan.     

Performance evaluation of full-scale upflow anaerobic sludge blanket reactor treating distillery spentwash

Performance of full-scale upflow anaerobic sludge blanket (UASB) reactors treating distillery spentwash was evaluated. The plant was designed to handle 650 m³ day⁻¹ of distillery spentwash having an average chemical oxygen demand (COD) concentration of 112,400 mg l⁻¹ with a HRT of 6 days. In the plant, the pH level of the influent varied from 3.50 to 4.40 but the pH of the treated effluent stabilized to a range of 7.36 to 7.68 during the study period. The operation of the reactors during study period revealed the stable conditions of the reactors, which is evident from the low COD, biochemical oxygen demand (BOD) and total solids (TS) contents in treated effluent. In the plant, the COD, BOD₅ and TS removal efficiencies were stabilized to the range of 62.19–66.59, 72.42–77.11, and 58.47–60.46%, respectively at an organic loading rate of 2.15–4.60 kg COD m⁻³ day⁻¹. The biogas production was stabilized to the range of 48,290–135,115 m³ week⁻¹ with 60% methane content. The total quantity of biogas produced ranged from 0.40 to 0.57, 1.04 to 1.71 and 0.40 to 0.56 m³ kg⁻¹ removals of COD, BOD and TS, respectively. This study concluded that the treatment of distillery spentwash using UASB reactors contributed significantly for pollution load reduction besides generating renewable in-house bio-energy.