Case studies in dynamic modelling of large-scale wastewater treatment plants

Several large-scale wastewater treatment plants have been modelled successfully using an extensive modelling library in the General Purpose Simulator, GPS-X. The mathematical models included all important processes on the selected wastewater treatment plants, i.e. primary sedimentation, activated sludge biokinetics and final clarification.The models have been used in different areas, such as: a)analysis of operational scenarios; b) determenation of sustained and peak capacity of plants(rated plant capacity) and c) investigation of plant expansion scenarios. Out of more than twenty documented cases four, involving simulation studies on large-scale wastewater plants are discussed.     

Comparison of three sequential extraction procedures to describe metal fractionation in anaerobic granular sludges

In the last few decades, several sequential extraction procedures have been developed to quantify the chemical status of metals in the solid phase. In this study, three extraction techniques (modified [A. Tessier, P.G.C. Campbell, M. Bisson, Anal. Chem. 51 (1979) 844]; [R.C. Stover, L.E. Sommers, D.J. Silvera, J. Water Pollut. Con. F. 48 (1976) 2165]; and the Bureau Communautaire de Reference (BCR) [K.F. Mossop, C.M. Davidson, Anal. Chim. Acta 478 (2003) 111]) were applied to study the distribution of trace (Co, Ni, Zn and Cu) and major (Mn and Fe) elements in two different anaerobic granular sludges from full-scale methanogenic wastewater treatment plants. The Stover scheme displayed a higher number of fractions that induces a poor recovery compared to the other schemes. The sequential extraction scheme recommended by BCR and the modified Tessier scheme gave similar trends and are sufficiently repeatable and reproducible for application in fractionation studies. However, the BCR scheme seems to be of limited utilisation to study anaerobic matrixes because the extraction stage for its reducible fraction may release substantial amounts of trace elements bound to the organic/sulfides fraction, and consequently, the recovery of trace elements in the oxide fraction may be overestimated at the expense of the oxidisable fraction. As a final conclusion, the modified Tessier scheme seems to be the most suitable scheme to study the metal partitioning in anaerobic granular sludges.     

Flow characteristics of primary and digested sewage sludge

Summary Rheological study of sewage sludge is useful for the design, operation and control of sewage treatment plants. The rheology is highly dependent on physical, chemical and biological characteristics of the sludge. A pipeline rheometer is described in this paper for measurement of rheological properties of the sludge. Primary sewage sludge is a complex flocculated suspension having no fixed particle dimension, shape, size distribution or surface characteristics. The information available so far on rheology of sewage sludge is not suitable for application in design because of the lack of data on physico-chemical characteristics of this sludge.Primary and digested sewage sludge are non-Newtonian in character. Both exhibit yield stress and while primary sludge is shear-thinning in nature, digested sludge has been found to be shear-thickening. Parabolic and yield-power law models have been used to express the experimental data obtained for sludges at various concentrations and temperatures. Yield stress of primary sludge varies exponentially with concentration and linearly with temperature within the short temperature range studied. Primary sludge is found to be antithixotropic at low shear stress. Digested sludge does not exhibit time dependency.With 9 figures and 5 tables     

Thermochemical and Toxic Element Behavior during Co-Combustion of Coal and Municipal Sludge

The thermochemical and kinetic behavior of co-combustion of coal, municipal sludge (MS) and their blends at different ratios were investigated by thermogravimetric analysis. Simulation experiments were performed in a vacuum tube furnace to determine the conversion behavior of toxic elements. The results show that the combustion processes of the blends of coal and municipal sludge are divided into three stages and the combustion curves of the blends are located between those of individual coal and municipal sludge samples. The DTG_max of the sample with 10% sludge addition reaches a maximum at the heating rate of 20 °C/min, indicating that the combustion characteristics of coal can be improved during co-combustion. Strong interactions were observed between coal and municipal sludge during the co-combustion. The volatilization rates of toxic elements decrease with an increasing proportion of sludge in the blends during co-combustion, which indicates that the co-combustion of coal and sludge can effectively reduce the volatilization rate of toxic elements. The study reflects the potential of municipal sludge as a blended fuel and the environmental effects of co-combustion of coal and municipal sludge.     

一种煤与两种城市污水污泥混合热解的热重分析

采用热重分析法对一种煤和两种城市污水污泥（S1和S2）及其混合物进行了热解实验研究,揭示了煤和污泥在氮气中的热解特性及污泥对煤热解特性的影响。煤和污泥的热解特性参数不同,主要表现在总失重率、失重速率及挥发分析出温度区间等。煤与污泥S1混合有助于增加样品的热解总失重率,提高失重速率;污泥S1与煤的挥发分析出区间部分重合,污泥灰中含的无机物对煤的热解起到催化效果;煤和S2污泥混合后热解反应过程中无明显相互作用;煤与城市污水污泥混合物的相互作用与样品特性和混合比例有关。     

Phenol Inhibition and Restoration of the Bioactivity of Anaerobic Granular Sludge

Inhibition and restoration of different concentrations of phenol on the bioactivity of anaerobic granular sludge were investigated with laboratory-scale equipment. It indicated that phenol concentration lower than 50 mg/l show no inhibitory effect on bioactivities of granular sludge. However, methane productivity, extracellular polymeric substances (EPS) content, and coenzyme F(420) activity were decreased by varying degrees when phenol concentration adopted for inhibition ranged between 50 and 400 mg/l. Noticeably, methane productivity could be fully or partly restored in case the phenol was removed after 24 h of phenol inhibition.     

Certified reference materials for organic contaminants in sewage sludge: a feasibility study

As an answer to the re-evaluation of the European sludge directive, two novel reference materials for organic components in municipal sludge have been produced and test certified for AOX (absorbable organic halogens), PAH (polycyclic aromatic hydrocarbons), NPE (nonylphenol and nonylphenolethoxylates), DEHP (di(2-ethylhexyl)phthalate), bisphenol A, and BFR (brominated flame retardants). The materials were prepared from raw sludge without spiking or mixing of different sludges. The study demonstrated that the technique for the preparation of a suitable reference material, sufficiently homogenous and stable, and with concentration levels that answer the needs of the laboratories and the relevant authorities, can now be presented in detail. The results, furthermore, show there is a need for method validation and standardisation of the measurements of NPEs and certain BFR congeners, and that the development of the laboratory structure in Europe, with fewer and more specialised laboratories, might become a major obstacle when trying to find a sufficient number of laboratories being appropriately proficient for this kind of study in the future.     

Synthesis of Hydrophobic Cationic Chitosan Flocculant and Its Sludge Dewatering Property

The hydrophobic cationic chitosan (HTCC) flocculant was synthesized by reacting chitosan with epoxy propyl trimethyl ammonium chloride (EPTAC) and (2,3-epoxy propyl) dodecyl dimethyl ammonium chloride (EDC), to improve its waste sludge dewaterability. By FTIR and ¹H NMR analysis, EPTAC and EDC were confirmed to be grafted onto the molecular chains of chitosan (CTS) successfully. With the increase of EDC content, G′ of HTCC aqueous solution with 1:1.5:1.5 mole ratio of CTS:EPTAC:EDC consistently showed higher values than G″ over the entire frequency range explored, indicating the formation of a physically cross-linked network. The crystallization ability of HTCC decreased compared with pristine CTS. The long alkyl chains on the EDC molecules enhanced the hydrophobicity of HTCC, and better dewaterability of the waste sludge was achieved through the promoted bridging action of HTCC.     

Comparative genomics for understanding the structure,function and sub-cellular localization of hypothetical proteins in Thermanerovibrio acidaminovorans DSM 6589 (tai)

The Thermanerovibrio acidaminovorans DSM 6589 (tai) is a unique bacterium isolated from anaerobic sludge bed reactor from sugar refinery in Netherland. The comparative genomic studies for understanding the hypothetical proteins in T. acidaminovorans DSM 6589 (tai) were carried out using different bioinformatic tools and web servers. In all 320 hypothetical proteins were screened from the total available genome. The Insilico function prediction for 320 hypothetical proteins was achieved by using different online servers like CDD-Blast, Interproscan and pfam whereas, the structure prediction for 202 hypothetical proteins were deciphered by using protein structure prediction server (PS2 server). The sub-cellular localization for the identified proteins was predicted by the use of cello v2.5 for 320. The study carried out has helped us to understand the structures and functions of unknown proteins available in T. acidaminovorans DSM 6589 (tai) through comparative genomic approach.     

Pharmaceuticals and Their Main Metabolites in Treated Sewage Sludge and Sludge-Amended Soil: Availability and Sorption Behaviour

This work evaluated the availability and sorption behaviour of four pharmaceuticals and eight of their metabolites in sewage sludge and sludge-amended soil. Digested sludge and compost were evaluated. The highest levels found in digested sludge corresponded to caffeine (up to 115 ng g⁻¹ dm), ibuprofen (45 ng g⁻¹ dm) and carbamazepine (9.3 ng g⁻¹ dm). The concentrations measured in compost were even lower than in digested sludge. No compound was detected in sludge-amended soils. This fact could be due to the dilution effect after sludge application to soil. Different adsorption capacities in sludge–soil mixtures were measured for the studied compounds at the same spike concentration. In general, except for paraxanthine and 3-hydroxycarbamazepine, the metabolite concentrations measured in the mixtures were almost two-fold lower than those of their parent compounds, which can be explained by their mobility and lixiviation tendency. The log K_d ranged from −1.55 to 1.71 in sludge samples and from −0.29 to 1.18 in soil–sludge mixtures. The log K_d values calculated for compost were higher than those calculated for digested sludge. The obtained results implied that the higher organic carbon content of compost could influence soil contamination when it is applied to soil.