A comparison of membrane bioreactor and conventional-activated-sludge mixed liquor and biosolids characteristics.

Characteristics and behavior of raw and digested mixed liquor derived from a membrane bioreactor (MBR) and a full-scale activated-sludge (FSAS) facility were compared. The accumulation of nondegradable chemical oxygen demand in the MBR appears to play an important role in increasing the observed biological yield coefficient (Y(obs)), reducing average floc size, decreasing total suspended solids/total solids and volatile suspended solids/volatile solids (VS) ratios, and reducing specific-oxygen-uptake rates of the mixed liquor relative to FSAS-derived biological solids. Membrane bioreactor sludges exhibited lower VS destruction following 30 days mesophilic-anaerobic and aerobic digestion when compared to FSAS sludges. Significant deterioration in dewatering behavior was observed for the FSAS biosolids after anaerobic digestion and, to a lesser extent, following aerobic digestion. In comparison, digestion had a small affect on dewatering efficiency and conditioner requirements for MBR biosolids. Full-scale facilities using membrane separation may need to tailor digestion and dewatering processes to the specific characteristics of MBR sludges.     

Use of acid preconditioning for enhanced dewatering of wastewater treatment sludges from the pulp and paper industry.

In municipal and industrial practices, wastewater treatment sludges are generally conditioned with organic polymers before dewatering. The dewatering polymers are expensive and contribute significantly to the overall sludge management cost. This paper discusses a preconditioning strategy that holds great promise for enhancing dewatering properties of wastewater treatment sludges, while reducing the cost. In this approach, the waste activated sludge (WAS) is briefly preconditioned with an acid before flocculating with an organic polymer. Experimental results showed that acid preconditioning significantly enhanced dewatering. Separately acidifying WAS and subsequently combining it with primary sludge produced higher presscake solids than acidifying the combined sludge to the same final pH. Acidification exhibited the added benefit of reducing Escherichia coli counts in sludge, thus improving its biological character. This may provide flexibility in choosing a beneficial use application.     

Disinfection and dewatering of wastewater solids by interstitial vapor generation.

Disinfection of wastewater solids (waste activated solids [WAS]) by interstitial vapor generation was investigated. In addition to the magnitude of disinfection, the amount of water removed and cost relative to traditional residuals disinfection processes was also examined. The process of interstitial vapor generation occurs as a result of the rapid heating of liquid in the interstices of the solid-liquid array. Intense heating causes boiling of the slurry liquid, resulting in an expanding vapor front that simultaneously dewaters the wastewater solids and contributes to the destruction of viable pathogenic microorganisms. Objectives of the study were threefold: (1) to validate disinfection of WAS using the interstitial vapor technique; (2) establish the degree of possible drying of the residuals using the techniques; and (3) establish the key operating variables for the process. Results showed a significant reduction in the most probable number of total coliforms and Escherichia coli (E. coli). Specifically, greater than four-log unit reductions were produced for both total coliform and E. coli bacteria. In addition to quantifying the reduction in bacteria, the percent solids were increased from an initial amount of 7.6% (mass basis) to a final solids content greater than 90% using optimal processing conditions. Cost comparisons were also conducted and shown to be quite favorable when compared with traditional disinfection methods such as lime addition. Because of the high level of E. coli reduction achieved, the process of interstitial vapor generation is shown to be capable of converting a class B biosolids into a class A pathogen reduced product. For example, an initial most probable number (MPN) of 1.2 x 10(6) E. coli bacteria were reduced to 19 at the extreme conditions of the process, well below the requirement of an MPN of 1000 for fecal coliform bacteria. Given its ability to disinfect and dewater wastewater solids, the interstitial vapor generation process was found to be a robust and beneficial technique to produce an environmental and publicly acceptable recyclable biosolids resource.     

Aluminium speciation in surface waters from a Welsh upland area

The complete aluminium speciation of surface waters from an acidified catchment, during dry weather and during storm episodes, is obtained. For the first time, estimates of adsorbed aluminium (Al(ad)) are reported together with other aluminium species. Al(ad) is calculated from the difference between monomeric aluminium content before and after separation of suspended solids by filtration (0.015 microm pore diameter). This fraction was very significant (Al(ad) >; 40 microg litre(-1)) for samples with high suspended solids content (ss >; 20 mg litre(-1)) collected during storm episodes. Plots of pAl(3+) versus pH for samples collected during dry weather are approximated by a straight line, close to the solubility line of synthetic gibbsite, and have a slope of 2.5, which suggests that these samples were saturated with respect to gibbsite. The cloud of pAl(3+) versus pH points for samples from storm episodes has a near zero slope, and shows a significant degree of undersaturation with respect to synthetic gibbsite. Various mechanisms of aluminium mobilisation are discussed.     

Effect of solids concentration on bacterial leaching of heavy metals from sewage sludge

Microbial metal leaching from sewage sludge (2-9% w/v) was carried out with the iron-oxidizing bacterium Thiobacillus ferrooxidans. Measurements of pH, oxidation-reduction potential, and concentration of Fe2+ indicated that T. ferrooxidans was effective in removing metals from an incubation bath containing less than 5% sludge solids concentration. Specifically, Cu leaching was completely suppressed at a high solids concentration of 9% (w/v). Results indicated that the deactivation of T. ferrooxidans at a high sludge content was mainly due to the presence of inhibiting materials such as organic matter. A mixed culture of sulfur-oxidizing bacteria was obtained by enrichment from anaerobically digested sewage sludge to enhance the efficiency of the microbial leaching process. These bacteria were much more effective in metal leaching than was iron-oxidizing T. ferrooxidans. At 9% (w/v) solids concentration, the leaching efficiencies of Zn and Cu were 78% (2.66 g/kg dry sludge) and 59% (1.36 g/kg dry sludge), respectively. Therefore, when removing heavy metals from the anaerobically digested sewage sludge, the indigenous sulfur-oxidizing bacteria isolated in the current study were more efficient than T. ferrooxidans, especially at high sludge solids concentrations.     

巢湖蓝藻的机械清除工艺以及藻水分离实验研究

对巢湖蓝藻进行机械清除以及藻水分离实验研究，实验采用的浮式围栏引导一机械清除．投加剥离液辅助机械清除工艺处理量大，除藻效率高，筛网过滤-浓缩-卧螺离心机脱水成藻泥的藻水分离工艺较为理想，藻泥含水率仅为89％。2011年5-10月在巢湖运用上述方法清除湖面水华蓝藻，共处理富藻水1．6万m3，得到藻泥970t，累计清除蓝藻106．7t（干重）。按照所清除蓝藻的总氮、总磷的平均含量计算，相当于从湖中移除了氮6．25t，磷2．1t。表明在富营养湖泊中水华蓝藻大量暴发时，采用上述方法除藻，对控制蓝藻水华污染，有效降低内源氮、磷等污染物负荷具有十分重要的作用。     

巢湖蓝藻的机械清除工艺以及藻水分离实验研究简

对巢湖蓝藻进行机械清除以及藻水分离实验研究，实验采用的浮式围栏引导-机械清除-投加剥离液辅助机械清除工艺处理量大，除藻效率高，筛网过滤-浓缩-卧螺离心机脱水成藻泥的藻水分离工艺较为理想，藻泥含水率仅为89%。2011年5—10月在巢湖运用上述方法清除湖面水华蓝藻，共处理富藻水1.6万m³，得到藻泥970 t，累计清除蓝藻106.7 t（干重）。按照所清除蓝藻的总氮、总磷的平均含量计算，相当于从湖中移除了氮6.25 t，磷2.1 t。表明在富营养湖泊中水华蓝藻大量暴发时，采用上述方法除藻，对控制蓝藻水华污染，有效降低内源氮、磷等污染物负荷具有十分重要的作用。     

酸处理对活性污泥脱水性能的影响及其作用机理

用硫酸对活性污泥进行脱水前预处理,可使污泥中水分分布发生有利于机械脱水的变化,即结合水含量减少、可脱水程度增大,从而改善活性污泥脱水效果.试验数据表明,只加阳离子PAM调理,污泥经过板框压滤脱水后(压榨时间30 min)泥饼含水率为76.14%;经过酸化预处理后再加阳离子PAM可以使泥饼含水率降至70.24%.不管是过滤脱水还是离心脱水过程,酸处理对污泥脱水速率没有太大影响,却可以提高污泥可脱水程度.进一步研究发现,酸处理的机理是:酸处理使污泥中胞外聚合物ECP水解、微生物细胞瓦解,从而絮体内部间隙水、细胞内部间隙水被释放变成自由水,污泥水分分布发生变化,污泥可脱水程度提高,最终导致污泥脱水效果好.     

Utilization of Dry Calcium Based Flue Gas Desulfurization Waste as a Hazardous Waste Fixation Agent

Several designated hazardous wastes (metal plating waste, oil sludge, heavy metal processing sludge) were studied relative to potential detoxification using dry calcium based FGD sludges. The FGD waste was generated from a pilot scale system which utilized slurried lime, a spray drier, and a bag filter. Following detailed physical and chemical identification of the raw FGD and hazardous wastes, various mixtures were prepared and cured. In all cases, even with the organic sludge, a rigid structural material evolved due to the pozzolanic reactions occurring from the wetted dry FGD waste. Structural characteristics, physical character, and chemical leaching effects were evaluated. The solids were leached via both EPA-RCRA and ASTM proposed leaching procedures. In all cases, the hazardous constituents were retained and not leached. Finally, the feasibility of using dry FGD wastes as fixating materials is discussed.     

Variability of aquifer sorption properties in a field experiment on groundwater transport of organic solutes: Methods and preliminary results

Methods to characterize the organic solute sorption distribution coefficient, organic carbon content, and specific surface area of aquifer solids from the site of a field experiment on solute transport in groundwater were refined for application to small subsamples of 10-cm depth increments taken from 5-cm diameter cores. Initial results indicate that the average sorption characteristics of the Borden aquifer do not vary appreciably along the trajectory of the solute plumes. However, the sorption distribution coefficient of tetrachloroethylene varied over nearly an order of magnitude among 10-cm depth increments in one core sample. Preliminary evidence suggests that the sorption distribution coefficients for four halogenated organic solutes vary proportionally among core strata. However, the distribution coefficients for sorption of tetrachloroethylene on various depth increments are not well correlated with either organic carbon content or specific surface area, suggesting that as yet unidentified mineral phases may play a significant role in sorption of such solutes by the sandy aquifer solids.     

Modelling of PCDD/F release from MSW bio-drying

In the present work, an experimentation was carried out to study the behaviour of PCDD/F during the process of municipal solid waste (MSW) bio-drying. This process belongs to the biological mechanical treatment (BMT) options and is aimed to the dewatering of MSW thanks to the biological exothermal reactions (thermal drying, on the contrary, needs an external heat source as methane). The result is a decrease of waste weight and an increase of lower heating value (as the energy content refers to a lower amount of waste). Of course, the overall energy availability does not increase, but the characteristics of bio-drying are interesting as a way for refuse derived fuel generation: glass, metals and inert removals are easier after bio-drying. The literature of the sector shows only few data on PCDD/F emission to air from BMT. Anyway, in the present work an original theory has been put forward in order to explain the enrichment of PCDD/F in the air exiting the biological processes. The role of the initial PCDD/F concentration in the ambient air entering the plant is obviously taken into account. The results of the developed experimentation and the following elaborations point out that PCDD/F could be freed from the volatile solids consumed during the process. The different amount of PCDD/F in the waste and the different consumption of volatile solids depending on the biological process can explain the different PCDD/F emission factors available in the literature.     

Effect of Solids Concentration on Bacterial Leaching of Heavy Metals from Sewage Sludge

Abstract

Microbial metal leaching from sewage sludge (2-9% w/v) was carried out with the iron-oxidizing bacterium Thiobacillus ferrooxidans. Measurements of pH, oxidation-reduction potential, and concentration of Fe²⁺ indicated that T. ferrooxidans was effective in removing metals from an incubation bath containing less than 5% sludge solids concentration. Specifically, Cu leaching was completely suppressed at a high solids concentration of 9% (w/v). Results indicated that the deactivation of T. ferrooxidans at a high sludge content was mainly due to the presence of inhibiting materials such as organic matter. A mixed culture of sulfur-oxidizing bacteria was obtained by enrichment from anaerobically digested sewage sludge to enhance the efficiency of the microbial leaching process. These bacteria were much more effective in metal leaching than was iron-oxidizing T. ferrooxidans. At 9% (w/v) solids concentration, the leaching efficiencies of Zn and Cu were 78% (2.66 g/kg dry sludge) and 59% (1.36 g/kg dry sludge), respectively. Therefore, when removing heavy metals from the anaerobically digested sewage sludge, the indigenous sulfur-oxidizing bacteria isolated in the current study were more efficient than T. ferrooxidans, especially at high sludge solids concentrations.     

Characteristics of biosolids in dimethyl ether dewatering method

In this study, a method for removing water from biosolids that uses dimethyl ether (DME) as an extractant was considered. This study evaluates the applicability of the DME dewatering method to biosolid cakes by using a DME flow-type experimental apparatus. It was found that a high dewatering ratio is clearly achieved by increasing the liquefied DME/biosolid ratio and lowering the liquefied DME linear velocity. As the liquefied DME/biosolid ratio was increased, the carbon content in dewatered biosolid showed a slight decrease and the TOC concentration in separated liquid increased significantly. Finally, the input energy Es to remove 1 kg of water from the biosolid cake, using both the DME dewatering method and the conventional drying method was estimated. The calculation shows that Es for the DME dewatering process is approximately a third of Es for the conventional thermal drying process.     

Water-extractable phosphorus in biosolids: implications for land-based recycling.

Phosphorus-based nutrient management will inevitably be required for land application of biosolids. Water-extractable phosphorus (WEP) in livestock manures is an indicator of phosphorus loss from agricultural watersheds and this study evaluated its use for biosolids. The WEP to total phosphorus percentage (PWEP) in 41 biosolids (representing a variety of wastewater and solids treatment processes) was compared to dairy and poultry manures and triple superphosphate fertilizer. The mean PWEP for conventionally treated and stabilized biosolids was 2.4%, which was significantly lower than inorganic fertilizer (85%), dairy manure (52%), and poultry manure (21%). Low biosolids PWEP is attributed to elevated aluminum and iron content from chemical additions during wastewater treatment and solids dewatering operations. Facilities using biological phosphorus removal had the highest mean biosolids PWEP (approximately 14%), whereas heat-dried biosolids had the lowest average PWEP (< approximately 0.5%). Paired samples of digested cake and the corresponding biosolids treated by processes to further reduce pathogens (i.e., thermal treatment, composting, and advanced alkaline stabilization) showed that these processes tended to reduce biosolids PWEP. Biosolids composition and processing mode exert a controlling influence on the potential for off-site phosphorus migration at land-application sites. Nutrient management policies for land-based recycling should account for the widely varying potential of organic amendments to cause soluble phosphorus losses in runoff and leaching.     

浅析某厂化学镀镍线的主要污染物及处理措施

某厂化学镀镍线产生的主要污染物为大气污染、水污染和固体废物污染。其中大气污染物主要为硫酸雾。水污染物为总镍、总铜、化学需氧量、悬浮物、总磷、氨氮等。固废废弃物均为危险废物,包括废包装材料、酸性废液、含镍废液。该文分析了化学镀镍线产生的废气、废水和固体废物的主要来源,并提出了防止污染的对策。     

Sorption of tylosin onto swine manure

Sorption of tylosin was conducted on manure solids (<2 mm) and colloidal materials (<1.2 microm) collected from open (OL) and covered (CL) anaerobic swine manure lagoons. The aqueous concentration of tylosin in the sorption studies bracket the levels expected in lagoons, between 1 mgl(-1) and 30 mgl(-1). Sorption isotherms were found to be slightly non-linear for 2 mm solids, with Freundlich distribution coefficients (K(f)) of 39.4 with n=1.32 for CL slurry and 99.5 with n=1.02 for OL. These values are comparable to those reported for loam soils, but higher than those reported for sandy or clay soils and lower than those reported for fresh manure. Normalization of K(d) to the organic carbon content of the solids gave K(oc) values of 570 lkg(-1) and 818 lkg(-1), for CL and OL solids, respectively. The K(d) and K(f) values were not significantly different between colloids and 2 mm solids in OL slurry, but were significantly different in CL due to the non-linearity of the colloid isotherm. Based on the K(d) values obtained and comparing the K(d) values of other antibiotics, tylosin is strongly sorbed to manure, and would be more mobile than tetracyclines, but less mobile than sulfonamides, olaquindox, and chloramphenicol. However, tylosin mobility may be facilitated through transport with colloidal manure materials.     

Influence of ozone pre-treatment on sludge anaerobic digestion: removal of pharmaceutical and personal care products

The effect of an oxidative pre-treatment with ozone on the removal of Pharmaceutical and Personal Care Products (PPCPs) during the anaerobic digestion of sewage sludge has been investigated. Besides, the digested sludge characteristics in terms of pathogens content, dewatering properties, heavy metals content and linear alkylbenzene sulfonates (LAS) were determined. During ozonation (20mg O(3)/g TSS), about 8% of volatile solids (VS) and 60% of the chemical oxygen demand (COD) were solubilized. However, no mineralization was observed. The elimination of VS and total COD during anaerobic digestion were not affected by ozone treatment with efficiencies ranging from 60% to 65%. All PPCPs considered were removed during anaerobic treatment of sludge, with efficiencies ranging from 20% to 99%. No significant influence of ozone pre-treatment was observed on PPCPs elimination except for carbamazepine. Pathogens, heavy metals and LAS contents after conventional and pre-ozonation treatment of sewage sludge were below the legal requirements. However, the dewatering properties of sludge were deteriorated when the ozone pre-treatment was applied.     

Case study II: application of the divalent cation bridging theory to improve biofloc properties and industrial activated sludge system performance-using alternatives to sodium-based chemicals.

The objective of this study was to investigate the application of the divalent cation bridging theory (DCBT) as a tool in the chemical selection process at an activated sludge plant to improve settling, dewatering, and effluent quality. According to the DCBT, to achieve improvements, the goal of chemical selection should be to reduce the ratio of monovalent-to-divalent (M/D) cations. A study was conducted to determine the effect of using magnesium hydroxide [Mg(OH)2] as an alternative to sodium hydroxide (NaOH) at a full-scale industrial wastewater treatment plant. Floc properties and treatment plant performance were measured for approximately one year during two periods of NaOH addition and Mg(OH)2 addition. A cost analysis of plant operation during NaOH and Mg(OH)2 use was also performed. During NaOH addition, the M/D ratio was 48, while, during Mg(OH)2 addition, this ratio was reduced to an average of approximately 0.1. During the Mg(OH)2 addition period, the sludge volume index, effluent total suspended solids, and effluent chemical oxygen demand were reduced by approximately 63, 31, and 50%, respectively, compared to the NaOH addition period. The alum and polymer dose used for clarification was reduced by approximately 50 and 60%, respectively, during Mg(OH)2 addition. The dewatering properties of the activated sludge improved dewatering as measured by decreased capillary suction time and specific resistance to filtration (SRF), along with an increase in cake solids from the SRF test. This corresponded to a reduction in the volume of solids thickened by centrifuges at the treatment plant, which reduced the disposal costs of solids. Considering the costs for chemicals and solids disposal, the annual cost of using Mg(OH)2 was approximately 30,000 dollars to 115,000 dollars less than using NaOH, depending on the pricing of NaOH. The results of this study confirm that the DCBT is a useful tool for assessing chemical-addition strategies and their potential effect on activated sludge performance.     

Case study I: application of the divalent cation bridging theory to improve biofloc properties and industrial activated sludge system performance-direct addition of divalent cations.

The objectives of this study were to examine the application of the divalent cation bridging theory (DCBT) to improve settling, dewatering, and effluent quality in pilot-scale reactors and a full-scale system treating an industrial wastewater. This was accomplished by lowering the monovalent-to-divalent (M/D) cation ratio by direct divalent cation addition. Research has shown that the M/D ratio is a potential indicator for settling and dewatering problems at wastewater treatment plants, and M/D ratios above 2 have been associated with poor settling, dewatering, and effluent quality. The M/D ratio of the wastewater in this study ranged from 6 to 20. The cations studied were calcium and magnesium. Results showed that the addition of calcium improved floc properties compared to control reactors with no calcium addition. The reductions in sludge volume index, effluent chemical oxygen demand (COD), and effluent total suspended solids (TSS) were approximately 35, 34, and 55%, respectively, when the M/D ratio was decreased to approximately 2:1. In addition, the cake solids from a belt filter press simulator increased by 72% and the optimum polymer dose required for conditioning was reduced by 70% in the reactor fed the highest calcium concentration when compared to control reactors with no calcium addition. The addition of calcium also decreased the negative effect of high filamentous organism numbers. In general, the addition of magnesium (Mg2+) had similar effects on effluent quality and dewatering properties, although some differences were measured. A full-scale test using calcium addition was performed. Measurements of effluent quality and floc properties were performed before, during, and after the calcium (Ca2+) addition period. The average M/D ratio during these periods was 6.2, 4.6, and 14.0, respectively. The addition of Ca2+ decreased the effluent five-day biochemical oxygen demand, effluent TSS, and effluent COD. The increased Ca2+ concentration also improved dewatering measured by a decrease in specific resistance to filtration and capillary suction time. Overall, the addition of divalent cations to the pilot- and full-scale activated sludge systems improved floc properties and the data fit well with the DCBT.     

Influence of suspended sediment on the biodegradation of chlorinated dibenzo-p-dioxins

Little is known of how the uptake and degradation of highly hydrophobic compounds, such as polychlorinated dibenzo-p-dioxins (PCDDs), by microorganisms is influenced by sorption of these compounds to sediment. In this study aqueous solutions of a mixture of 2-chloro-, 1,3-dichloro-, 2,8-dichloro- and 1,2,4-trichlorodibenzo-p-dioxins were first incubated for 24 days with 100 mg/l suspended sediment. Subsequently, the degradation of the PCDDs in these sediment suspensions by Alcaligenes sp. strain JB1 was compared to that in solutions which did not contain sediment. The amounts of all four compounds degraded in the sediment suspensions after 168 h were greater than those initially present in the dissolved phase, based on their calculated sediment-water partition coefficients. The sorbed fractions were therefore sufficiently readily desorbed to be partly degraded. However, the biodegradation rates were lower in the sediment suspensions than in the solutions.