Effect of dissolved organic material and cations on freeze-thaw conditioning of activated and alum sludges

Freeze-thaw conditioning effectively dewaters alum and activated sludges, but it works better on alum sludge than it does on activated sludge. The main difference between alum sludge and activated sludge is that activated sludge has high concentrations of both dissolved organic material and ions. Dissolved organic material and ions may possibly alter the freezing process and decrease the effectiveness of freeze-thaw conditioning on activated sludge. The objective of this study is to investigate the effect of dissolved organic material and cations on freeze-thaw conditioning of sludges, and to improve the effectiveness of freeze-thaw conditioning on activated sludge. The results of this study show that although protein, carbohydrate and cation concentrations in activated sludge supernatant are initially high, they dramatically increase after freeze-thaw conditioning. The increase is likely to come from the release of extracellular and intracellular material to sludge supernatant. The observed increase in the DNA concentration in activated sludge supernatant after freeze-thaw conditioning indicates that freeze-thaw causes cell disruption. Alum sludge supernatant, on the other hand, initially contains low concentrations of proteins, carbohydrates and cations which do not noticeably change after freeze-thaw conditioning. When ECPs (extracellular polymers) and cations are extracted from activated sludge before freeze-thaw conditioning, the sludge settles and dewaters better after the freeze-thaw. The resulting aggregates are smaller and denser resembling the “coffee ground” aggregates of alum sludge.     

A respirometric study of the influence of aliphatic alcohols on activated sludges

The influences of primary aliphatic alcohols on oxygen consumption of activated sludges in endogenous states were measured using a laboratory respirometer. The alcohols studied were n-propanol to n-octanol. Using beef extract as a reference substrate, results demonstrated a two-stage action for all the primary alcohols studied. It was found that these alcohols enhanced the dissolved oxygen uptake rate by the biomass when they were below critical concentrations, but had inhibiting effects above these concentrations. The critical concentration has been observed to decrease with increasing size of the alcohol molecule. The results obtained are explained in terms of modifications to lipid membranes observed by other workers.     

Purification and characterization of extracellular polysaccharide from activated sludges

A three stage purification process has been developed for soluble, activated-sludge exocellular polymers which results in a polysaccharide fraction substantially free of nucleic acids and protein, with the residual protein probably bound as a glycoprotein. Characterization and comparison of purified exopolysaccharide fractions from five different effluent treatment works revealed many similarities both in terms of monomer composition and molecular weight distribution. Only five monomers were detected, namely: glucose, galactose, mannose, glucuronic acid and galacturonic acid, and all the polysaccharide fractions were of high molecular weight, ranging from 3 × 10⁵ to 2 × 10⁶.     

Pressurised electro-osmotic dewatering of activated and anaerobically digested sludges: electrical variables analysis

Pressurised electro-osmotic dewatering (PEOD) of two sewage sludges (activated and anaerobically digested) was studied under constant electric current (C.C.) and constant voltage (C.V.) with a laboratory chamber simulating closely an industrial filter. The influence of sludge characteristics, process parameters, and electrode/filter cloth position was investigated. The next parameters were tested: 40 and 80 A/m², 20, 30, and 50 V—for digested sludge dewatering; and 20, 40 and 80 A/m², 20, 30, and 50 V—for activated sludge dewatering. Effects of filter cloth electric resistance and initial cake thickness were also investigated.The application of PEOD provides a gain of 12 points of dry solids content for the digested sludge (47.0% w/w) and for the activated sludge (31.7% w/w). In PEOD processed at C.C. or at C.V., the dewatering flow rate was similar for the same electric field intensity. In C.C. mode, both the electric resistance of cake and voltage increase, causing a temperature rise by ohmic effect. In C.V. mode, a current intensity peak was observed in the earlier dewatering period. Applying at first a constant current and later on a constant voltage, permitted to have better control of ohmic heating effect. The dewatering rate was not significantly affected by the presence of filter cloth on electrodes, but the use of a thin filter cloth reduced remarkably the energy consumption compared to a thicker one: 69% of reduction energy input at 45% w/w of dry solids content. The reduction of the initial cake thickness is advantageous to increase the final dry solids content.     

Modeling of chlorine effect on floc forming and filamentous micro-organisms of activated sludges

Chlorination is the most economical, non-specific method to control the excessive growth of filamentous micro-organisms causing bulking in activated sludge systems in the treatment of food industrial wastewaters; it was one of the first methods used to control filamentous bulking and is still widely employed. Considering that chlorination affects both floc-forming and filamentous micro-organisms and leaves undesirable disinfection by-products, it is necessary to define the adequate doses to control bulking, minimizing the effect on floc-forming bacteria.In the present work the effect of biomass concentration and type of micro-organism on chlorine decay kinetics was evaluated; the inactivation of either a filamentous (Sphaerotilus natans) or a floc-forming (Acinetobacter anitratus) micro-organism due to chlorination was also analyzed.For chlorine decay assays, the samples were treated in a batch system with sodium hypochlorite ranging between 9.8 and 56.6 mg Cl(2) (gVSS)(-1). Respirometric assays were used to evaluate the effect of chlorine on micro-organisms respiratory activity; in these cases, sodium hypochlorite doses ranged between 2.5 and 18 mgCl(2) (gVSS)(-1).A model that allowed to predict simultaneously chlorine consumption and respiratory activity decay for both micro-organisms as a function of time was proposed. The model includes three coupled differential equations corresponding to respiratory inhibition, readily organic matter oxidation by chlorine and chlorine decay. The rate of chlorine decay depended on both, type and concentration of the micro-organisms in the system. Chlorine consumption rate due to S. natans was 2-4 times faster than A. anitratus. Using the proposed model initial critical chlorine doses (the lowest initial dose that leads to a total inhibition of the respiratory activity) were calculated for both micro-organisms and values of 11.9 mgCl(2) (gVSS)(-1) for S. natans and 4.5 mgCl(2) (gVSS)(-1) for A. anitratus were obtained. These critical doses indicated that in non flocculated pure cultures, floc-former bacteria A. anitratus was more susceptible to chlorine action than S. natans.     

Evolution of size distribution and transfer of mineral particles between flocs in activated sludges: an insight into floc exchange dynamics

The aggregation behavior of activated sludge flocs was investigated by monitoring the size distribution of flocs and transfer of mineral particles between flocs, under various conditions of agitation and dilution. The results showed that (i) the shape of the floc size distribution can be fitted with a gamma function, (ii) a steady-state mean floc size is reached for a given stirring rate, (iii) this stable floc size is shifted towards floc growth as sludge concentration is increased, (iv) under cycled-shear conditions, microbial aggregates break up and re-form in an almost reversible manner, (v) blending of raw sludge and sludge spiked with Aquatal mineral particles results in particle exchange between flocs and (vi) the detailed study of exchange kinetics indicates that some flocs do not participate to the aggregation dynamics. These experimental results suggest that the activated sludge floc size is governed by a flocculation/deflocculation balance, implying an exchange of floc constituents between microbial aggregates.     

毛面灰砂砖的开发研究

普通灰砂砖砌筑面密实,光滑,导致灰砂砖与砂浆的粘结强度被削弱,砌体抗剪强度差。研制成功的毛面灰砂砖上,下表面分别带有许多细小的弧形条状凹槽和小半球状压痕,增大了砖表面粗糙度,可使砌体粘结抗剪强度比普通灰砂砖提高４０％左右。指出：带弧形条状凹槽的上表面和带小半球压痕的下表面相粘结的组合是最佳砌筑方式;生产毛面灰砂砖生产成本增加极少,强度不受影响,砌筑时坐浆方便,砖块不会游动,是一种改善和提高灰砂砖砌     

Variations of respiratory activity and glutathione in activated sludges exposed to low ozone doses

Ozonation is one of the most effective treatments for reducing the production of activated sludges in wastewater treatment plants. However, because microorganisms are present in the form of microcolonies, some bacteria may be exposed to sub-lethal ozone doses that could lead to adaptation and resistance to further exposition to oxidative treatment. This represents a major question as it may limit the effect of the treatment, especially when low ozone doses are applied. The critical ozone dosage, defined as the lowest specific transferred ozone concentration leading to a decrease in the maximum oxygen uptake rate was estimated to range between 0.9 and 13.6mg O(3)g(-1) COD(sludges), according to the sludges tested. The lowest ozone dosage leading to the decrease of GSH and GSHt concentrations could be estimated to be lower than 10mg O(3)g(-1) COD(sludges) for GSH, and close to 10mg O(3)g(-1) COD(sludges) for GSHt. After sludge exposure to low ozone doses, no higher amounts of glutathione were synthesized, suggesting that no development of resistance to ozonation occurred after sludge treatment with low ozone doses.     

Study of different ratios of primary and waste activated sludges to enhance the methane yield

This work aimed the study of methane yield using different proportions of primary sludge (PS) and waste activated sludge (WAS) for anaerobic digestion (AD) conversion. Three trials were carried out: T1 (60 : 40, v/v), T2 (80 : 20, v/v) and T3 (100 : 00, v/v) to estimate the best proportion in comparison with a reference scenario, T0 (40 : 60, v/v). AD was performed in mesophilic conditions with a hydraulic retention time (HRT) of 15 days and an organic loading rate (OLR) expressed in total volatile solids (TVS) of 1.62 ± 0.06 kg_TVS m^?3 day^?1. Biogas production for trials T1 and T2 increased from 45 to 71% in comparison with T0. The experimental methane production along trials was used to assess the energy recovery corresponding to increases from 32 to 55%. The most suitable trial to be implemented at real‐scale is T1, applying a lower PS solid retention time combined with an increase of WAS thickening.     

3-nitrobenzenesulfonic acid and 3-aminobenzesulfonic acid in a laboratory trickling filter: Biodegradability with different activated sludges

The biodegradation of 3-nitrobenzenesulfonate (3-NBS) or 3-aminobenzenesulfonate (3-ABS) was examined in a laboratory trickling filter device containing one of six activated sludges as the biocatalyst. No activated sludge from four communal treatment plants could degrade 3-NBS or 3-ABS. In contrast, each of the sludges from two plants treating wastes from the textile industry was able to completely degrade 3-NBS or 3-ABS. Under certain conditions, communal activated sludge could acclimate to degrade 3-NBS, even though inoculation with a degradative sludge was a more efficient process. In the absence of a carbon source, the degradative ability of trickling filters was retained for at least 1 week; thereafter, an adaptation phase was required before rapid and extensive degradation of recovered 3-NBS. Degradation was monitored by global parameters (DOC and release of CO₂) and specific determinations of substrate (HPLC). The global parameters indicated incomplete metabolism of 3-NBS, but this effect was found to be due to the presence of a non-degraded impurity (5%), 4-NBS, found in most commercial preparations of 3-NBS.     

Anaerobic digestion of seven different sewage sludges: A biodegradability and modelling study

Seven mixed sewage sludges from different wastewater treatment plants, which have an anaerobic digester in operation, were evaluated in order to clarify the literature uncertainty with regard to the sewage sludge characterisation and biodegradability. Moreover, a methodology is provided to determine the Anaerobic Digestion Model No. 1 parameters, coefficients and initial state variables as well as a discussion about the accuracy of the first order solubilisation constant, which was obtained through biomethane potential test. The results of the biomethane potential tests showed ultimate methane potentials from 188 to 214 mL CH₄ g⁻¹ COD_fed, COD removals between 58 and 65% and two homogeneous groups for the first order solubilisation constant: (i) the lowest rate group from 0.23 to 0.35 day⁻¹ and (ii) the highest rate group from 0.27 to 0.43 day⁻¹. However, no statistically significant relationship between the ultimate methane potential or the disintegration constant and the sewage sludge characterisation was found. Next, a methodology based on the sludge characterisation before and after the biomethane potential test was developed to calculate the biodegradable fraction, the composite concentration and stoichiometric coefficients and the soluble COD of the sewage sludge; required parameters for the implementation of the Anaerobic Digestion Model No. 1. The comparison of the experimental and the simulation results proved the consistency of the developed methodology. Nevertheless, an underestimation of the first order solubilisation constant was detected when the experimental results were simulated with the solubilisation constant obtained from the linear regression experimental data fitting. The latter phenomenon could be related to the accumulation of intermediary compounds during the biomethane potential assay.     

石灰土冻胀特性试验研究

为考察石灰土在冻结状态下的物理力学性质 ,对不同石灰含量的石灰土的冻胀特性进行了试验研究。试验结果表明 ,石灰土的孔隙度和导水系数随着石灰含量的增加不断减小 ,而黏聚力则不断增加。在这种情况下 ,石灰土的冻胀率随着石灰含量的增加呈现显著减小的趋势。综合其它有关因素 ,从防止冻胀的角度来看 ,石灰含量的最优值约为 12 %～ 15 %左右     

山砂蒸压灰砂砖试验研究

阐述了山砂的理化性能,通过调整山砂颗粒级配,添加外加剂,控制用水量等措施,研制成功技术性能符合要求的10级山砂蒸压灰砂砖,为山砂的开发利用提供了依据。     

Experimental study on adsorption capacity of an activated carbon-based adsorption water chiller

The objective of this study was to evaluate the adsorption capacity of a working pair for an adsorption water chiller. Activated carbon fibre–methanol, activated carbon fibre–ethanol and activated carbon pallet–ethanol were used as an adsorbent–adsorbate pair in this study. The experiment was conducted using a stainless steel adsorber, 110?mm diameter by 150?mm height, filled with adsorbent and transparent plastic evaporator, 100?ml capacity, filled with adsorbate. The experiment was performed by isobaric adsorption in the temperature range of 10–100°C at the evaporator temperature of 20°C (water chiller). An experimental investigation showed that the activated carbon fibre–methanol pair has the highest adsorption capacity (0.44?kg/kg) compared to the activated carbon fibre–ethanol and activated carbon pallet–ethanol pairs. The finding revealed that uniform structure and large surface area of adsorbent as well as low boiling point and large latent heat of adsorbate had highly significant effects on adsorption capacity. The effect of time and adsorber temperature on adsorption capacity is also discussed in this study.     

浅谈高速公路石灰稳定土的施工控制

基于路基施工技术的规范,结合某高速公路当地特殊的土质,总结了石灰稳定土施工工艺,并提出灰土施工的质量控制要点,从而确保该地区高速公路石灰稳定土的施工质量。     

消石灰对SMA的高温性能影响的试验研究

通过锥入度试验分析了消石灰对SMA中玛脂高温性能的影响,并以SMA-13为基础,通过车辙试验研究了掺消石灰对SMA高温性能的影响,最后分析了玛脂锥入度与混合料动稳定度的相关性,以达到改善SMA水稳定性的目的。     

热回收型多元变制冷剂流量空调系统控制策略实验研究

阐述了多元变制冷剂流量(MVRV)空调系统的自治协调控制(SRI)思想,指出室外机叠加循环原理是自治协调控制的核心内容;自行研制出热回收型MVRV空调系统实验装置并建立实验台,对上述策略进行验证。实验结果表明,所提出的控制策略切实可行,效果良好,适用于单冷、热泵以及热回收型MVRV空调系统。     

Effect of polyelectrolyte conditioning on the enhanced dewatering of activated sludge by application of an electric field during the expression phase

Activated sludge is known to be poorly dewaterable due to its high surface charge density and the extreme solids compressibility, even after polyelectrolyte conditioning. The application of an electric field during pressure dewatering (PDW) of sludge can enhance the dewaterability by the electroosmosis effect. A comparative study was conducted to investigate the additional effect of an electric field, applied during the expression phase, on the dewatering course of polyelectrolyte conditioned sludge, compared to mere PDW. It was found that the application of an electric field markedly improved the dewatering kinetics for all sludge samples, regardless of the conditioning treatment. Although the conditioning polyelectrolyte characteristics and dose had a major effect on the PDW of sludge, the conditioning history did not have a significant effect on the electroosmotic water transport efficiency during the sludge expression phase. By means of on-line streaming potential measurements and fractionated filtrate electrophoretic mobility measurements, it could be demonstrated that even at high polyelectrolyte doses, leading to positively charged sludge flocs, negative surface charges were still present inside the sludge matrix. During the expression of the sludge cake, when liquid is forced to move through the floc inside pores, these negative surface charges hampered PDW, but enhanced electroosmotic dewatering. Electroosmosis is therefore an appropriate technique to remove the water fraction that is associated with these negative surface charges.     

Rutting evaluation of hydrated lime and SBS modified asphalt mixtures for laboratory and field compacted samples

The purpose of this study is to evaluate permanent deformation for hydrated lime and SBS modified asphalt mixtures. Control (C), 2% hydrated lime (2L), 5% SBS polymer mixtures and 2%hydrated lime–5%SBS (2L5SBS) mixtures were prepared. The Laboratoire Central des Ponts et Chaussées (LCPC) wheel tracker, also known as French Rutting Tester were realized with two different stages. Same LCPC slabs were produced. Original LCPC compactors and also field cylinder were used separately. LCPC rutting values were determined with left and right wheel loadings. Also averages were obtained with calculation. Repeated creep tests were used for these mixtures and permanent deformations were plotted for two different moisture conditioning that water immersion and freeze and thaw cycles. Diameter samples (100 mm and 150 mm) were studied in repeated creep tests. In the result that LCPC tracking values were compared with repeated creep tests in terms of sample diameters. LCPC wheel-tracking test results show that 2L5SBS mixtures reveal utmost performance according to the other mixtures types. Polymer modification increased rutting resistance of lime modified ones. Both original LCPC compactor and field cylinder compaction showed resemble results. 150 mm samples showed highest correlation (higher than R² = 0.80) between LCPC test and repeated creep test for different compaction types and different moisture conditionings.     

石灰改良膨胀土微孔结构试验研究

0　引　　言 用石灰改良黏性土的工程性质、抑制膨胀土的胀缩性是岩土工程中常用的方法,但对于其机理以及掺灰量的确定,过去因技术的限制,多采用化学和力学的方法作过较多的研究[1～3],而对于膨胀土加灰前后微孔结构的变化及改性机理一直不是十分清楚。本文从黏性土的微孔结构角度,采用美国产的ASAP-2010M+C表面吸附仪(该仪器在国外对矿物学和表面化学领域的相关研究较多[4～6],且仅局限于矿物晶体结构和表面,而对土体的微孔和膨胀性的讨论未见诸各文献),对在实验室中放置了8a的石灰土压实土样进行了表面吸附试验研究,测得了土样加灰前后的BET比表面积、BJH微孔比表面积、BJH微孔体积、微孔孔径及孔径