Thermochemical liquidization and anaerobic treatment of dewatered sewage sludge

Dewatered sewage sludge was thermochemically liquidized at 175°C and the liquidized sludge was separated by centrifugation to 57.7% (w/w) supernatant [moisture, 92.3%; volatile solid (VS), 7.0%] and 42.3% precipitate (moisture, 71.6%; VS, 18.9%). The supernatant was successfully anaerobically digested. Biogas yield from the supernatant at organic loading concentrations of 1.9–2.2 g VS/l during 9 days' incubation was 440 ml/g-added VS and digestion ratio was 66% (w/w). Biogas yield in the case of dewatered sewage sludge was 257% ml/g-added VS and digestion ratio was 45%. Digestion of the supernatant resulted in high biogas productivity and a high digestion ratio compared with that of the dewatered sewage sludge. Moreover, it was suggested that the precipitate can be incinerated without the need for any supplemental fuel.     

The investigation of effect of organic carbon sources addition in anaerobic–aerobic (low dissolved oxygen) sequencing batch reactor for nutrients removal from wastewaters

The effect of addition of organic carbon sources (acetic acid and waste activated sludge alkaline fermentation liquid) on anaerobic–aerobic (low dissolved oxygen, 0.15–0.45 mg/L) biological municipal wastewater treatment was investigated. The results showed that carbon source addition affected not only the transformations of polyhydroxyalkanoates (PHA), glycogen, nitrogen and phosphorus, but the net removal of nitrogen and phosphorus. The removal efficiencies of TN and TP were, respectively, 61% and 61% without organic carbon source addition, 81% and 95% with acetic acid addition, and 83% and 97% with waste activated sludge alkaline fermentation liquid addition. It seems that the alkaline fermentation liquid of waste biosolids generated in biological wastewater treatment plant can be used to replace acetic acid as an additional carbon source to improve the anaerobic–aerobic (low dissolved oxygen) municipal wastewater nutrients removal although its use was observed to cause a slight increase of effluent BOD and COD concentrations.     

Sorption and Release of Organics by Primary,Anaerobic, and Aerobic Activated Sludge Mixed with Raw Municipal Wastewater

New activated sludge processes that utilize sorption as a major mechanism for organics removal are being developed to maximize energy recovery from wastewater organics, or as enhanced primary treatment technologies. To model and optimize sorption-based activated sludge processes, further knowledge about sorption of organics onto sludge is needed. This study compared primary-, anaerobic-, and aerobic activated sludge as sorbents, determined sorption capacity and kinetics, and investigated some characteristics of the organics being sorbed. Batch sorption assays were carried out without aeration at a mixing velocity of 200 rpm. Only aerobic activated sludge showed net sorption of organics. Sorption of dissolved organics occurred by a near-instantaneous sorption event followed by a slower process that obeyed 1^st order kinetics. Sorption of particulates also followed 1^st order kinetics but there was no instantaneous sorption event; instead there was a release of particles upon mixing. The 5-min sorption capacity of activated sludge was 6.5±10.8 mg total organic carbon (TOC) per g volatile suspend solids (VSS) for particulate organics and 5.0±4.7 mgTOC/gVSS for dissolved organics. The observed instantaneous sorption appeared to be mainly due to organics larger than 20 kDa in size being sorbed, although molecules with a size of about 200 Da with strong UV absorbance at 215–230 nm were also rapidly removed.     

Effects and model of alkaline waste activated sludge treatment

Due to lack of information about alkaline sludge treatment with high dose at ambient temperature, alkaline sludge treatment was investigated to know the effects of different doses (0-0.5 mol/L) of sodium hydroxide (NaOH) and calcium hydroxide [Ca(OH)2] at 0-40 degrees C. Results showed that NaOH was more suitable than Ca(OH)2 for sludge disintegration. For NaOH treatment, most efficient dose was about 0.05 mol/L (0.16 g/g dry solid), and 60-71% solubilization of organic matters was achieved in first 30 min during its treatment of 24h. The process is described by a transmutative power function model, and relation between reaction rate constant and temperature are according with Arrhenius equation. Low dose NaOH treatment (<0.2 mol/L) deteriorated sludge dewatering ability obviously, while the ability was recovered gradually with the increase of NaOH dose. For Ca(OH)2 treatment, the disintegrated floc fragments and soluble organic polymers can be re-flocculated with the help of calcium cations. Consequently sludge disintegration effect was counteracted and dewatering ability improved.     

Extraction and environmental risk assessment of heavy metal in the municipal dewatered sludge using rhamnolipid treatment

Heavy metal could lead to serious environmental risk to the ecosystem, destroy human health via the food chain. The heavy metal removal from sludge is an emergent issue. In this work, rhamnolipid, an environment-friendly material, was used to enhance heavy metal extraction from the sludge. The results showed that Cu, Zn, Cr, Pb, Ni, and Mn maximum extraction efficiencies were 35.10 ± 2.31%, 45.33 ± 3.24%, 27.58 ± 3.35%, 24.12 ± 3.51%, 43.31 ± 2.53% and 22.10 ± 2.11%, respectively; most of exchangeable and reducible fractions, and partly oxidizable and residual fractions have been extracted by the rhamnolipid solution. After treatment, I_R values of heavy metals increased in the treated sludge, the I_R values for Cu, Zn, Cr, Pb, Ni, and Mn were 0.24 ± 0.01, 0.25 ± 0.03, 0.21 ± 0.02, 0.32 ± 0.03, 0.22 ± 0.021 and 0.41 ± 0.03, respectively. M_F values indicated that heavy metal mobility order was Zn>Ni>Cu>Mn>Cr>Pb in the treated sludge. According to the two risk assessment methods (risk assessment code, RAC and potential ecological risk index, PERI), the risk assessment of heavy metal was investigated in the after treatment sludge, which indicated that rhamnolipid could extract the mobility of heavy metal and lead to no or low risk to the ecosystem. Therefore, rhamnolipid was utilized to enhance heavy metal extraction from dewatered sludge in this study, which is a promising technique for heavy metal extraction from the dewatered sludge.     

Effect of Drying Process on Heavy Metals Fractionation of Contaminated Sludge for Land Application

Metal fractionation studies on metals in sludge are usually done on dried sludge. Although there are advantages in this form of sludge, it is possible that fractionation of metals in sludge may be influenced by the drying process, which consequently affects mobility of metals at disposal. In this study, sequential chemical extraction was done to assess the effect of drying on fractionation of cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni), and zinc (Zn) on wet and dewatered (air-dried and oven-dried) anaerobically digested sludge samples in Bangkok, Thailand. Results revealed an insignificant difference in the fractionation profile of metals for both wet and dewatered sludge. The higher percentage of residual fraction for Cu and oxidizable fraction for Zn in the wet sludge, however, makes this form more suitable for direct land application. In the case of oven-dried and air-dried sludge, the forms of some metals (e.g., Pb and Zn) seem to vary significantly as the sludge is oven-dried, with Pb decreasing its residual phase by 15%, and Zn increasing in oxidizable phase by 41%. The results seem to indicate that drying affects bioavailability of metals in sludge and air-drying seems to favor sludge for land application.     

Use of protozoa and metazoa for decreasing sludge production in aerobic wastewater treatment

Summary A new approach to decreasing sludge production in aerobic biological wastewater treatment involving use of protozoa and metazoa was tested. The dissolved organics in the two synthetic wastewaters (based on acetic acid and methanol, respectively) tested were decomposed to >90% and the biomass production was decreased by 60–80%. The total sludge yield, expressed as total suspended solids per gram chemical oxygen demand removed, was 0.17 g TSS/g COD in the system fed acetic acid, whereas it was 0.05 g TSS/g COD in the system fed methanol. The explanation for this difference was that in the system fed methanol, dispersed bacteria were obtained that were easily grazed by the protozoa and metazoa in the predator stage. In the system fed acetic acid, the bacteria formed zoogloeal flocs, which protected them from grazing in the predator stage. With both carbon sources a significant release of nitrate (> 7 mg N/l) and of phosphate (> 2.5 mg P/l) was observed in the effluent.     

Anaerobic digestion of glycerol derived from biodiesel manufacturing

The anaerobic digestion of glycerol derived from biodiesel manufacturing, in which COD was found to be 1010 g/kg, was studied in batch laboratory-scale reactors at mesophilic temperature using granular and non-granular sludge. Due to the high KOH concentration of this by-product, H₃PO₄ was added to recover this alkaline catalyst as agricultural fertilizer (potassium phosphates). Although it would not be economically viable, a volume of glycerol was distilled and utilised as reference substrate. The anaerobic revalorisation of glycerol using granular sludge achieved a biodegradability of around 100%, while the methane yield coefficient was 0.306 m³ CH₄/kg acidified glycerol. Anaerobic digestion could be a good option for revalorising this available, impure and low priced by-product derived from the surplus of biodiesel companies. The organic loading rate studied was 0.21–0.38 g COD/g VSS d, although an inhibition phenomenon was observed at the highest load.     

Studies on the production of Scytalidium acidophilum biomass

Summary The conversion of nutrient-supplemented and non-supplemented acid-extracts from peat to biomass of the acid-resistant fungus Scytalidium acidophilum is described. Yeast extract and several inorganic salts were tested as nutrient supplement to the peat extract in shake-flask experiments and in an agitated and aerated fermentor. The best results were obtained in the fermentor, with 0.3% yeast extract, which produced 6.2 g dry biomass/1 with a yield of 41% and an efficiency of 30%, at 200 rpm and 1.75 vvm in 8 days. Although higher agitation speeds appeared detrimental to the mycelial physiology, it was detected that the dissolved oxygen concentration at 200 rpm could limit the growth of S. acidophilum if higher biomass concentrations are obtained. The potential for utilizing the residual fermentation medium as a plant liquid fertilizer is reported.     

Anaerobic storage as a pretreatment for enhanced biodegradability of dewatered sewage sludge

Dewatered sewage sludge is often stored still before further processing and final disposal. This study showed that anaerobic storage of dewatered sewage sludge could hydrolyze organic matter from the sludge matrix, and increase soluble organic acid content from 90 to 2400 mg/L and soluble organic carbon content from 220 to 1650 mg/L. Correspondingly, the contents of proteins, celluloses and hemicelluloses were reduced by 2-9%. Applying anaerobic storage markedly enhanced the efficiency of the subsequent bio-drying process on stored sludge. Correspondingly, biogas and odor gas were produced immediately after commencing the sludge storage. Anaerobic storage with odor control can be applied as a pretreatment process for dewatered sewage sludge in wastewater treatment plants.     

A complete industrial system for economical succinic acid production by Actinobacillus succinogenes

An industrial fermentation system using lignocellulosic hydrolysate, waste yeast hydrolysate, and mixed alkali to achieve high-yield, economical succinic acid production by Actinobacillus succinogenes was developed. Lignocellulosic hydrolysate and waste yeast hydrolysate were used efficiently as carbon sources and nitrogen source instead of the expensive glucose and yeast extract. Moreover, as a novel method for regulating pH mixed alkalis (Mg(OH)₂ and NaOH) were first used to replace the expensive MgCO₃ for succinic acid production. Using the three aforementioned substitutions, the total fermentation cost decreased by 55.9%, and 56.4 g/L succinic acid with yield of 0.73 g/g was obtained, which are almost the same production level as fermentation with glucose, yeast extract and MgCO₃. Therefore, the cheap carbon and nitrogen sources, as well as the mixed alkaline neutralize could be efficiently used instead of expensive composition for industrial succinic acid production.     

Evaluation of extractants for soil humic substances

Summary An evaluation of alkaline extractants was done by isotachophoresis and compared with infrared, ultraviolet and visible spectroscopic analysis. The electrophoretograms show that the humic acid extracted. This result is partially corroborated by the E₄/E₆ ratio. Differences in the carboxyl content and TRIS. In the pyrophosphate humic acid three fractions of high molecular weight were not extracted. This resultis partially corroborated by the E₄/E₆ ratio. Differences in the carboxyl content found by ir spectra of the TRIS humic acid and the NaOH humic acid were not shown in the isotachophoretic separation.     

Rapid determination of zearalenone in edible oils by HPLC with fluorescence detection

A fast, cost-efficient, sensitive and accurate assay method for zearalenone in edible oils is described, as an alternative to gel permeation chromatography (GPC). Oil samples were extracted with an alkaline mixture of methanol and water (methanol +10 g/l aqueous ammonium carbaminate solution, pH 9; 9 + 1, v+v). The pH of the extract was neutralized with hydrochloric acid and then concentrated to dryness. The residue was dissolved with HPLC solvent, and zearalenone was determined by high-performance liquid chromatography with fluorometric detection (HPLC-FLD). The method was successfully validated for two matrices, maize oil and rapeseed oil. The recovery rate was 87%, and the coefficient of variation was 2.8% in a rapeseed oil sample contaminated with 27 μg zearalenone/kg. At a signal-to-noise ratio of 3:1, the method detection limit was 10 μg/kg, which was considered to be adequate in view of the present European Union maximum level of 400 μg/kg.     

腐植酸肥料对生姜土壤微生物量和酶活性的影响

设4个处理:空白对照、等量腐植酸、等量无机养分和腐植酸复合肥.通过小区试验,研究了腐植酸肥料在生姜不同生育时期对土壤微生物量和3种重要酶活性的影响.结果表明:与不施肥处理比较,施用腐植酸使前期的微生物量碳增加、脲酶活性降低,后期的微生物量碳减少、脲酶活性提高;施用腐植酸增加土壤活跃微生物量、提高酸性磷酸酶活性、降低蔗糖酶活性,全生育期平均土壤活跃微生物量和酸性磷酸酶活性分别提高17.34%和11.40%、蔗糖酶活性降低10.57%.与施用等量无机养分处理比较,施用腐植酸复合肥也使前期的微生物量碳增加、脲酶活性降低,后期的微生物量碳减少、脲酶活性提高;施用腐植酸复合肥增加土壤活跃微生物量、提高酸性磷酸酶和蔗糖酶活性,全生育期平均土壤活跃微生物量、酸性磷酸酶和蔗糖酶活性分别提高18.61%、10.07%和7.61%.     

利用污泥提取液制备微生物絮凝剂

以污水厂剩余污泥作为培养基原料,经过一系列处理,探索微生物絮凝剂产生菌的最适发酵培养基配方,结果表明,污泥预处理条件以pH 12碱解条件最优,碳氮源产出量最大,补加8 g/L葡萄糖后灭菌,微生物絮凝剂产生菌LLin6可正常产絮,絮凝率达91.55%。该结果为降低微生物絮凝剂的制备成本,并实现污泥的减量化和污泥资源化利用提供了基础。     

The lability of zinc humate species

Abstract

At low pH, interaction between zinc(II) ions and humic acids yields sparingly soluble surface complexes; in alkaline conditions there are soluble complexes which differ in stability, stoichiometry and lability. The distribution of zinc between ‘fixed’, ‘non-labile’ and ‘labile’ complex forms at different pH values has been evaluated by equilibrating Zn-loaded humic acid (20 to 300 nmol μmol^?1) with ion exchange resins of different types (and counter ion forms). Analysis of the supernatant aqueous phase determined the non-labile soluble zinc content (at the equilibrium pH); the ‘labile’ fraction value was found by back-extracting the washed resins into 0.05 M EDTA (pH 7). When the system pH was <6, about 5% was released as a soluble non-labile complex and the majority of the Zn remained firmly fixed to the solid phase. Above pH 6, the substrate dissolved and the percentage present as non-labile species increased from 5 to 70% as the pH changed from 5 to 8.5. Around pH 7, the labile content peaked at around 90%, but this fraction value dropped to ?20% at pH 8.5 (due in part to a lower affinity of zinc for the functional groups on the resin involved). The type of synthetic exchanger used controlled both the system pH and the degree of complex dissociation. The distribution pattern was also influenced by the amount of Zn(II) sorbed on the substrate, the initial weight of humic acid present, and the mixing time (dissolution of the solid phase was slow in acid media). While the ratio of fixed to soluble forms could control migration of the metal ion in environmental systems, it is the labile content which is more likely to be ‘available’ to living matter.     

The impact of different operating conditions on membrane fouling and EPS production

The main goal of this research was to investigate how different factors influence membrane fouling. The impact of the different concentrations of activated sludge and the amount of extracellular polymer substances (EPS) were monitored. Two pilot plants with submerged membrane modules (hollow fiber and flat sheet) were operated and the raw wastewater was used.Humic substances were identified as the major components of EPS in the activated sludge (more than 34%) in both pilot plants. As the basic constituent in permeate, humic substances were identified as the most dominant components in the effluent (61%) in both pilot plants. Conversely, proteins were mostly analyzed in permeate and supernatant below the detection limit. The total amount of EPS [mg g⁻¹ (VSS)] was similar for concentrations of activated sludge 6, 10 and 14 g L⁻¹. Carbohydrates were identified as the component of EPS which tends most to clog membranes.     

Two stages of treatments for upgrading bleached softwood paper grade pulp to dissolving pulp for viscose production

To convert bleached softwood paper grade pulp into dissolving pulp for viscose application, two stages of treatments consisting of enzymatic treatment and alkaline peroxide treatment were investigated. It was found that high reactivity (about 80%) of pulp could be achieved by endoglucanases (EG)-rich industrial cellulase treatment, and the α-cellulose content as well as the viscosity of enzymatically treated pulp can be further adjusted by the alkaline peroxide treatment with certain dosages of NaOH and H₂O₂ to finally meet the quality requirements of dissolving pulp. The resulting pulp with 68.7% of reactivity, 92.1% of α-cellulose content, and 506.9 mL/g of pulp viscosity could be obtained after the two stages of treatments. The appropriate dosage of EG-rich cellulase was 300 IU/g bone dry pulp in the stage of enzymatic treatment, while the suitable dosages of NaOH and H₂O₂ were 9 wt% and 1 wt%, respectively, in the stage of alkaline peroxide treatment.     

Nutritional Requirements of Methanosarcina sp. Strain TM-1

Methanosarcina sp. strain TM-1, an acetotrophic, thermophilic methanogen isolated from an anaerobic sludge digestor, was originally reported to require an anaerobic sludge supernatant for growth. It was found that the sludge supernatant could be replaced with yeast extract (1 g/liter), 6 mM bicarbonate-30% CO₂, and trace metals, with a doubling time on methanol of 14 h. For growth on either methanol or acetate, yeast extract could be replaced with CaCl₂ · 2H₂O (13.6 μM minimum) and the vitamin p-aminobenzoic acid (PABA, ca. 3 nM minimum), with a doubling time on methanol of 8 to 9 h. Filter-sterilized folic acid at 0.3 μM could not replace PABA. The antimetabolite sulfanilamide (20 mM) inhibited growth of and methanogenesis by Methanosarcina sp. strain TM-1, and this inhibition was reversed by the addition of 0.3 μM PABA. When a defined medium buffered with 20 mM N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid was used, it was shown that Methanosarcina sp. strain TM-1 required 6 mM bicarbonate-30% CO₂ for optimal growth and methanogenesis from methanol. Cells growing on acetate were less dependent on bicarbonate-CO₂. When we used a defined medium in which the only organic compounds present were methanol or acetate, nitrilotriacetic acid (0.2 mM), and PABA, it was possible to limit batch cultures of Methanosarcina sp. strain TM-1 for nitrogen at NH₄⁺ concentrations at or below 2.0 mM, in marked contrast with Methanosarcina barkeri 227, which fixes dinitrogen when grown under NH₄⁺ limitation.     

Distribution of heavy metals in a sewage oxidation pond and their adsorption in residual solid (sewage sludge ash)

Abstract

Electrometric studies were carried out on the interaction of heavy metal ions such as manganese, chromium, nickel, copper, zinc, cadmium and lead with the extracted organic matter, humic and fulvic acid from the sludge in a sewage oxidation pond. The distribution of heavy metals was between 60 and 97%, which is associated with the solid waste (sludge) of the oxidation pond. The adsorption/removal efficiency of metal ions onto the sludge ash was more than 90% and 97%, respectively, in the pure system. To obtain the ash, the sludge was burnt at 500°C, treated with nitric acid (1+1) to leach out all the metals and then filtered; the residue left on the filter paper was the pure ash. Both this and that coated with organic matter were studied. The adsorption isotherm for metals, humic/fulvic acids and metal-humic/fulvic acid complexes in the metal-free sludge ash and in the organic matter in the pure system were studied using the Freundlich relationship. Good agreement was found suggesting that sediment and humic/fulvic acids have an important role in the mobility, dispersion and sedimentation of metal ions in an aquatic environment. More of these heavy metals are removed in the pure system than in the natural system. This may be due to the lesser availability of humic and fulvic acids in the lagoons during the short detention time of sewage in suspension in the oxidation pond, whereas the sludge which has settled to the bottom of the pond for several years contains rich decomposed organic matter in the form of humic and fulvic acids containing heavy metals. Such pure systems could be useful for the effective removal of heavy metals.