Heavy metal fractionation and organic matter stabilization in sewage sludge treatment wetlands

The presence of heavy metals in sludge stabilized in a reed bed system may affect its use for agricultural purposes. However, the environmental impact of sludge depends on the availability and phytotoxicity of these heavy metals.The aim of this research was to determine the effectiveness of a reed bed (Phragmites australis) sludge treatment system in two urban wastewater treatment plants in Italy after a three-year period of operation: (i) by estimating the process of sludge stabilization, following conventional and nonconventional parameters related to the evolution of organic matter quality (water soluble carbon, dehydrogenase activity, pyrolytic fragments); (ii) by following the heavy metal bioavailability in the sludge through their fractionation. For heavy metal fractionation, the Community Bureau of Reference (BCR) was followed.The results showed that there was mineralization and stabilization of sludge over time, suggested by the decrease of about 35% in water soluble carbon and of about 60-80% of dehydrogenase activity. Moreover, significant values of benzene (17%), toluene (31%) and phenol (9%) were found at the end of experimentation in both treatment wetlands, highlighting the re-synthesis of humic-like matter.The results also showed that the content of heavy metals after 30 months was associated with the less mobile fractions of the sludge (more than 60% of total heavy metal content for almost metal), in particular, the fraction linked to the organic matter.     

Biofuels from continuous fast pyrolysis of soybean oil: A pilot plant study

The continuous fast pyrolysis of soybean oil in a pilot plant was investigated. The experimental runs were carried out according to an experimental design alternating the temperature (from 450 to 600 °C) and the concentration of water (from 0% to 10%). The liquid products were analyzed by gas chromatography and by true boiling point (TPB) distillation. A simple distillation was used to obtain purified products such as gasoline and diesel. Physical–chemical analysis showed that these biofuels are similar to fossil fuels. Mass and energy balances were carried out in order to determine the vaporization enthalpy and the reaction enthalpy for each experiment. The thermal analysis showed that it is possible to use the products as an energy source for the process.     

Extraction and hydrolysis of levoglucosan from pyrolysis oil

Fermentable sugar obtained from lignocellulosic material exhibits great potential as a renewable feedstock for the production of bio-ethanol. One potentially viable source of fermentable sugars is pyrolysis oil, commonly called bio-oil. Depending on the type of lignocellulosic material and the operating conditions used for pyrolysis, bio-oil can contain upwards of 10 wt% of 1,6-anhydro-β-d-glucopyranose (levoglucosan, LG), an anhydrosugar that can be hydrolyzed to glucose. This research investigated the extraction of levoglucosan from pyrolysis oil via phase separation, the acid-hydrolysis of the levoglucosan into glucose, and the subsequent fermentation of this hydrolysate into ethanol.Optimal selection of water-to-oil ratio, temperature and contact time yielded an aqueous phase containing a levoglucosan concentration of up to 87 g/L, a yield of 7.8 wt% of the bio-oil. Hydrolysis conditions of 125 °C, 44 min and 0.5 M H₂SO₄ resulted in a maximum glucose yield of 216% (when based on original levoglucosan), inferring other precursors of glucose were present in the aqueous phase. The aqueous phase contained solutes which inhibited fermentation, however, up to 20% hydrolysate solutions were efficiently fermented (yield = 0.46 g EtOH/g glucose; productivity = 0.55 g/L h) using high yeast inoculums (1 g/L in flask) and micro-aerophilic conditions.     

Remediation of chromite ore processing residue by pyrolysis process with sewage sludge

The present work developed a novel technique to treat chromite ore processing residue (COPR). The process involved mixing the COPR with sewage sludge followed by pyrolysis. The gaseous organic fraction generated during pyrolysis of sludge was beneficial to Cr(VI) reduction. Process variables, such as the amount of sludge added to COPR (sludge-to-COPR (S/C) ratio), heating temperature, reaction time and particle size, were systematically varied, and their influences on the Cr(VI) reduction in COPR were investigated. Cr(VI) content had decreased greatly, from 3384 mg kg⁻¹ for untreated COPR to less than 30 mg kg⁻¹ for COPR treated at 600 °C.     

污水处理厂污泥膨胀和污泥发泡的比较分析

活性污泥法由于操作简单、处理效果好被广泛应用于市政污水和工业废水的处理。污泥膨胀和污泥发泡现象影响二次沉淀池的泥水分离过程和生物反应池的微生物量稳定,严重困扰着污水处理厂的正常运行,被称为污水处理厂的"癌症"。本文从污泥膨胀和污泥发泡的定义及分类出发,全面地比较了表征污泥膨胀和污泥发泡的方法、引起污泥膨胀和污泥发泡的丝状细菌种类及控制污泥膨胀和污泥发泡方法的异同,并探讨了污泥膨胀和污泥发泡问题的未来研究方向和控制策略,期望能够为今后污泥膨胀和污泥发泡问题的研究和调控提供有价值的参考。     

A kinetic model for production of glucose by hydrolysis of levoglucosan and cellobiosan from pyrolysis oil

Anhydro sugars, produced during wood pyrolysis, can by hydrolyzed to sugars under acidic conditions. The acid hydrolysis of two common anhydro sugars in wood pyrolysis oils, levoglucosan (1,6-anhydro-beta-D-glucopyranose) and cellobiosan (beta-D-glucopyranosyl-(1-->4)-1,6-anhydro-D-glucopyranose), was investigated. Levoglucosan hydrolysis to glucose follows a first-order reaction, with an activation energy of 114 kJ mol(-1). For cellobiosan hydrolysis, 44% of the cellobiosan is hydrolyzed initially via the beta-(1-->4) glycosidic bond to form levoglucosan and glucose. The remaining cellobiosan is hydrolyzed initially at the 1,6 anhydro bond to form cellobiose. Both reactions are first order with respect to cellobiosan, with an activation energy of 99 kJ mol(-1). The intermediate levoglucosan and cellobiose are hydrolyzed to glucose.     

Liquid hydrocarbon fuels obtained by the pyrolysis of soybean oils

The pyrolysis reactions of soybean oils have been studied. The pyrolytic products were analyzed by GC–MS and FTIR and show the formation of olefins, paraffins, carboxylic acids and aldehydes. Several kinds of catalysts were compared. It was found that the amounts of carboxylic acids and aldehydes were significantly decreased by using base catalysts such as Na₂CO₃ and K₂CO₃. The low acid value pyrolytic products showed good cold flow properties and good solubility in diesel oil at low temperature. The results presented in this work have shown that the pyrolysis of soybean oils generates fuels that have chemical composition similar to petroleum based fuels.     

Water extraction of pyrolysis oil: the first step for the recovery of renewable chemicals

The interest in biomass as a source of renewable energy and chemicals has been increasing in keeping up with the transition to a sustainable bio-based economy. An important initial step of chemicals recovery from biomass-derived pyrolysis oil is water extraction where most of polar compounds are isolated in the aqueous phase. This study was done to investigate the effects of stirring rate and water-to-oil ratio on the extraction capability (distribution coefficient and yield), water content, and atomic composition of both aqueous and organic phases. The results show that the stirring rate above 300 rpm has no influence on the equilibrium. Increasing the water-to-oil ratio dilutes the aqueous phase without changing the atomic distribution. Forest residue-derived pyrolysis oil should be extracted at a water-to-oil ratio of 0.65-0.7, whereas pine-derived pyrolysis oil is preferably extracted at the lowest feasible water-to-oil ratio where complete phase separation occurs, which is 0.5 in this study.     

Efficacy of tar oil recovered during slow pyrolysis of macadamia nut shells

Decay and termite resistance of wood treated with tar oil obtained from a commercial pyrolysis process of macadamia nut shells was evaluated. Vacuum-treated pinewood specimens were subjected to two brown- and two white-rot fungi based on the soil-block test method specified by the American Wood Protection Association after a 10-day-leaching process. Treated specimens were also subjected to the subterranean termite attack according to Japanese Industrial Standards (JIS) for 3 weeks under laboratory conditions. In the study, growth inhibition of selected fungi with the tar oil was also tested in vitro. Treated wood specimens at a retention level of 460 kg m⁻³ showed good protection against all the fungi tested. Mass losses in leached specimens were less than those observed in unleached specimens. Similar results were seen when the specimens were subjected to termite attack. Inhibition tests showed that higher concentrations of the tar oil are critical for inhibition of the brown-rot fungi compared to the concentrations required to impede the white-rot and sap-staining fungi tested.     

Electricity generation from bio-treatment of sewage sludge with microbial fuel cell

A two-chambered microbial fuel cell (MFC) with potassium ferricyanide as its electron acceptor was utilized to degrade excess sewage sludge and to generate electricity. Stable electrical power was produced continuously during operation for 250 h. Total chemical oxygen demand (TCOD) of sludge was reduced by 46.4% when an initial TCOD was 10,850 mg/l. The MFC power output did not significantly depend on process parameters such as substrate concentration, cathode catholyte concentration, and anodic pH. However, the MFC produced power was in close correlation with the soluble chemical oxygen demand (SCOD) of sludge. Furthermore, ultrasonic pretreatment of sludge accelerated organic matter dissolution and, hence, TCOD removal rate in the MFC was increased, but power output was insignificantly enhanced. This study demonstrates that this MFC can generate electricity from sewage sludge over a wide range of process parameters.     

Properties of oil and char derived from slow pyrolysis of Tetraselmis chui

Pyrolysis of biomass is a means to industrially manufacture renewable oil and gas, in addition to biochar for soil amendment and long-term carbon fixation. In this work, oil and char derived from the slow pyrolysis of the unicellular marine diatom Tetraselmis chui are analysed using a variety of techniques. The pyrolytic oil fraction exhibits a wide variety of fatty acids, alkanes, alkenes, amides, aldehydes, terpenes, pyrrolidinines, phytol and phenols, with a high heating value (HHV) of 28 MJ/kg. The biochar produced has a HHV of 14.5 MJ/kg and reveals a number of properties that are potentially valuable from an agronomic point of view, including high cation exchange capacity (CEC), large concentration of N, and a low C:N ratio. The quantity of C in T. chui biochar that can be expected to stabilise in soil amounts to approximately 9%/wt of the original feedstock, leading to a potential net reduction in atmospheric CO₂.     

The microbial community composition of a nitrifying-denitrifying activated sludge from an industrial sewage treatment plant analyzed by the full-cycle rRNA approach

The composition of the microbial community present in the nitrifying-denitrifying activated sludge of an industrial wastewater treatment plant connected to a rendering facility was investigated by the full-cycle rRNA approach. After DNA extraction using three different methods, 94 almost full-length 16S rRNA gene clones were retrieved and analyzed phylogenetically. 59% of the clones were affiliated with the Proteobacteria and clustered with the beta- (29 clones), alpha- (24), and delta-class (2 clones), respectively. 15 clones grouped within the green nonsulfur (GNS) bacteria and 11 clones belonged to the Planctomycetes. The Verrucomicrobia, Acidobacteria, Nitrospira, Bacteroidetes, Firmicutes and Actinobacteria were each represented by one to five clones. Interestingly, the highest 'species richness' [measured as number of operational taxonomic units (OTUs)] was found within the alpha-class of Proteobacteria, followed by the Planctomycetes, the beta-class of Proteobacteria, and the GNS-bacteria. The microbial community composition of the activated sludge was determined quantitatively by using 36 group-, subgroup-, and OTU-specific rRNA-targeted oligonucleotide probes for fluorescence in situ hybridization (FISH), confocal laser scanning microscopy and digital image analysis. 89% of all bacteria detectable by FISH with a bacterial probe set could be assigned to specific divisions. Consistent with the 16S rRNA gene library data, members of the beta-class of Proteobacteria dominated the microbial community and represented almost half of the biovolume of all bacteria detectable by FISH. Within the beta-class, 98% of the cells could be identified by the application of genus- or OTU-specific probes demonstrating a high in situ abundance of bacteria related to Zoogloea and Azoarcus sensu lato. Taken together, this study provides the first encompassing, high-resolution insight into the in situ composition of the microbial community present in a full-scale, industrial wastewater treatment plant.     

Biofuel production from palm oil with supercritical alcohols: effects of the alcohol to oil molar ratios on the biofuel chemical composition and properties

Biofuel production from palm oil with supercritical methanol (SCM) and supercritical ethanol (SCE) at 400 °C and 15 MPa were evaluated. At the optimal alcohol to oil molar ratios of 12:1 and 18:1 for the SCM and SCE processes, respectively, the biofuel samples were synthesized in a 1.2-L reactor and the resulting biofuel was analyzed for the key properties including those for the diesel and biodiesel standard specifications. Biofuel samples derived from both the SCM and SCE processes could be used as an alternative fuel after slight improvement in their acid value and free glycerol content. The remarkable advantages of this novel process were: the additional fuel yield of approximately of 5% and 10% for SCM and SCE, respectively; the lower energy consumption for alcohol preheating, pumping and recovering than the biodiesel production with supercritical alcohols that use a high alcohol to oil molar ratio of 42:1.     

Dynamics of the microfauna community in a full-scale municipal wastewater treatment plant experiencing sludge bulking

We investigated the dynamics of the microfauna community in activated sludge, with special reference to sludge bulking, in two parallel municipal wastewater treatment systems in Beijing, China over a period of 14 months. Annual cyclic changes in microfauna community structures occurred in both systems. RELATE analysis based on Spearman's Rank correlation indicated that microfauna community structures were highly correlated with the sludge volume index (SVI) (p < 0.001), which indicates sludge settleability. Nutrient conditions of raw sewage (p < 0.01) and hydraulic retention time (HRT) (p < 0.05) were also related to microfauna community structures. Abundances of the species Epistylis plicatilis and Vorticella striata increased significantly with an increase in SVI (p < 0.001) and decrease in water temperature (p < 0.001), suggesting that sludge bulking may have created favorable conditions for the two species, even under unfavorable temperature conditions. Sludge de-flocculation primarily due to the excessive growth of Microthrix parvicella-like filaments could be an important driving force for the microfauna community changes. The release of flocculated non-filamentous bacteria may represent a suitable food source for these species. The two species may be considered as potential bioindicators for sludge bulking.     

Kinetic studies of overlapping pyrolysis reactions in industrial waste activated sludge

A sludge pyrolytic kinetics model was established in this study. Two types of sewage sludge from different industrial wastewater treatment plant produced different DTG (Derivative Thermogravimetry) shapes with an overlapping pattern. The multi-heating rate method was conducted to evaluate the kinetics for obtaining reasonable pyrolysis mechanisms and DTG curves were divided into several peaks using the Lorentz fitting method based on the composition of the sludge and the desire for precision. The peaks formed corresponded to the pyrolysis reactions of volatile matter, microbe cells, proteins, inorganic substances and char respectively, which can be reasonably explained based on the results from the flue gas analyzer and the chemical analysis. Two types of sewage sludge were found to have similar pyrolysis mechanisms. Reasonable reasons were also given to explain the distortion and lag observed in the DTG curves and pyrolysis mechanism.     

Spatial distribution of dynamics characteristic in the intermittent aeration static composting of sewage sludge

Spatial differences and temporal changes in biological activity characteristics were investigated in a static reactor using intermittent aeration during the sewage sludge composting process. Pumice was proposed as a bulking agent in the composting of sewage sludge. Variations in temperature, moisture, oxygen level, volatile solids, specific oxygen uptake rate (SOUR) and dehydrogenase activity (DHA) were determined during 28 days of composting. The peak temperature in the upper region of the reactor was 10 °C higher than that at the bottom. The moisture level in the middle region was significantly higher than that of other positions. Analysis of SOUR and DHA indicated that the lowest level of sludge stability was at the bottom region. These spatial and temporal differences in biochemical dynamics in the static system could extend the composting period and affect product uniformity.     

Detection of coliphages and enteroviruses in sewage and aerosol from an activated sludge wastewater treatment plant

Coliphages and enteroviruses were monitored over 12 months in sewage and air adjacent to an activated sludge plant. Both showed temporal variation but the mean count of phages in enterovirus-positive samples was not significantly different from that in enterovirus-negative samples. Hence coliphages are not necessarily a good indicator of enteroviruses in sewage and aerosols.     

Codigestion of olive oil mill wastewaters with manure, household waste or sewage sludge

Combined anaerobic digestion of oil mill effluent(OME) together with manure, household waste (HHW) orsewage sludge was investigated. In batch experimentsit was shown that OME could be degraded into biogaswhen codigested with manure. In codigestion with HHWor sewage sludge, OME dilution with water (1:5) wasrequired in order to degrade it. Using continuouslystirred lab-scale reactors it was shown thatcodigestion of OME with manure (50:50 and 75:25 OMEto manure ratios) was successful with a theoreticalOME utilization of 75% and with approx. 87%reduction of the lipids content in OME. An OMEutilization of approx. 55%, and lipid reduction of73% was reached in codigestion with HHW (50:50 and75:25 OME to HHW ratios). The results showed thatthe high buffering capacity contained in manure,together with the content of several essentialnutrients, make it possible to degrade OME withoutprevious dilution, without addition of externalalkalinity and without addition of external nitrogensource.     

Increased biogas production at wastewater treatment plants through co-digestion of sewage sludge with grease trap sludge from a meat processing plant

The feasibility of co-digesting grease trap sludge from a meat-processing plant and sewage sludge was studied in batch and reactor experiments at 35 degrees C. Grease trap sludge had high methane production potential (918 m(3)/tVS(added)), but methane production started slowly. When mixed with sewage sludge, methane production started immediately and the potential increased with increasing grease trap sludge content. Semi-continuous co-digestion of the two materials was found feasible up to grease trap sludge addition of 46% of feed volatile solids (hydraulic retention time 16d; maximum organic loading rate 3.46 kgVS/m(3)d). Methane production was significantly higher and no effect on the characteristics of the digested material was noticed as compared to digesting sewage sludge alone. At higher grease trap sludge additions (55% and 71% of feed volatile solids), degradation was not complete and methane production either remained the same or decreased.     

Functioning and toxicity of artificial soil mixtures with metal-bearing sewage sludge

Various artificial soil mixtures were prepared by mixing two different toxic metals containing sewage sludge from Ljubljana and Maribor wastewater treatment plants with natural mineral soil. The plots with mixtures were exposed to field environmental conditions for a period of 1 year, after which we assessed soil toxicity (germination test with Lactuca sativa), potential metal phyto-accessibility (diethylenetriamine pentaacetic acid – DTPA extraction test), soil functioning (by soil enzymes activity) and conducted a field growth test with Lollium perenne L. as a metal bio-indicator plant. The metal phyto-accessibility extraction test (DTPA) showed lower values than the metal accumulation test with L. perenne L., which also showed higher metal concentrations in roots compared to leaves. With the exception of the mixture containing 30% (w/w) of sludge from the Ljubljana wastewater treatment plant, all mixtures containing more than 20% of sludge negatively affected root elongation of L. sativa seeds, indicating an increase in artificial soils toxicity. Increasing the ratio of sludge from the Ljubljana plant increased dehydrogenase and decreased phosphomonoesterase, while the addition of sludge from the Maribor plant increased phosphomonoesterase activity. Overall, the effect of sludge addition on artificial soil properties, toxicity and functioning not only depended on dosage but was also sensitive to the source and pre-treatment of the sewage sludge.