Co-conditioning of the anaerobic digested sludge of a municipal wastewater treatment plant with alum sludge: benefit of phosphorus reduction in reject water.

In this study, alum sludge was introduced to co-conditioning and dewatering with an anaerobic digested sludge from a municipal wastewater treatment plant, to examine the role of the alum sludge in improving the dewaterbility of the mixed sludge and also in immobilizing phosphorus in the reject water. Experiments have demonstrated that the optimal mix ratio for the two sludges is 2:1 (anaerobic digested sludge:alum sludge: volume basis), and this can bring approximately 99% phosphorus reduction in the reject water through the adsorption of phosphorus by alum in the sludge. The phosphorus loading in wastewater treatment plants is itself derived from the recycling of reject water during the wastewater treatment process. Consequently, this co-conditioning and dewatering strategy can achieve a significant reduction in phosphorus loading in wastewater treatment plants. In addition, the use of the alum sludge has been shown to beneficially enhance the dewaterability of the resultant mixed sludge, by decreasing both the specific resistance to filtration and the capillary suction time. This is attributed to the alum sludge acting in charge neutralization and/or as adsorbent for phosphate in the aqueous phase of the sludge. Experiments have also demonstrated that the optimal polymer (Superfloc C2260, Cytec, Botlek, Netherlands) dose for the anaerobic digested sludge was 120 mg/L, while the optimal dose for the mixed sludge (mix ratio 2:1) was 15 mg/L, highlighting a huge savings in polymer addition. Therefore, from the technical perspective, the co-conditioning and dewatering strategy can be viewed as a "win-win" situation. However, for its full-scale application, integrated cost-effective analysis of process capabilities, sludge transport, increased cake disposal, additional administration, polymer saving, and so on, should be factored in.     

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.     

The digestibility of waste activated sludges.

Laboratory digestion studies using waste activated sludges (WAS) were conducted to compare the digestion performance between anaerobic and aerobic processes. Nine samples of WAS from seven wastewater treatment plants were collected and batch-digested under both anaerobic and aerobic conditions for 30 days at 25 degrees C. The cation content of wastewater (both floc and solution phases) and solution biopolymer (protein and polysaccharide) was measured before and after digestion and compared with volatile solids destruction data. The study revealed that each digestion process was associated with a distinct biopolymer fraction, which accounted for differences in volatile solids reduction under anaerobic and aerobic conditions. The anaerobic digestion data showed strong correlations between soluble protein generation, ammonium production, percent volatile solids reduction, and floc iron (Fe). These data suggest that the amount of volatile solids destroyed by anaerobic digestion depends on the Fe content of floc. In aerobic digestion, polysaccharide accumulated in solution along with calcium and magnesium. For aerobic digestion, correlations between divalent cation release and the production of inorganic nitrogen were found. This implies that divalent cation-bound biopolymer, thought to be lectin-like protein, was the primary organic fraction degraded under aerobic conditions. The results of the study show that the cation content in wastewater is an important indicator of the material that will digest under anaerobic or aerobic conditions and that some of the volatile solids will digest only under either anaerobic or aerobic conditions.     

The effect of wastewater cations on activated sludge characteristics: effects of aluminum and iron in floc.

Wastewater samples collected from seven wastewater treatment plants (WWTPs) were characterized to assess the impacts of wastewater cations on the activated sludge process. The cations included in this study were sodium (Na+), potassium, ammonium, calcium, magnesium, aluminum (Al), and iron (Fe). Among the selected cations, Al and Fe were of most interest to this study because their role in bioflocculation has not been extensively studied and remains largely unknown. The data showed that WWTPs contained highly varying concentrations of Na+, Al, and Fe in the wastewater and that these cations were responsible for differences between WWTPs as to sludge dewatering rates and effluent quality. In general, a high influent Na+ concentration caused poor sludge dewatering and effluent characteristics. However, when sufficient Al and Fe were present in floc, the deleterious effects of Na+ were offset. The data associated with Al further revealed that waste activated sludge with low Al contained high concentrations of soluble and colloidal biopolymer (protein + polysaccharide), resulting in a high effluent chemical oxygen demand, high conditioning chemical requirements, and poor sludge dewatering properties. These results suggest that Al will improve activated sludge effluent quality by scavenging organic compounds from solution and binding them to floc.     

Temporal evolution of polycyclic aromatic hydrocarbons (PAHs) in sludge from wastewater treatment plants: comparison between PAHs and heavy metals

This paper presents results on the presence and temporal variability of the 16 PAHs recommended by the EPA in primary, secondary and digested sewage sludge over a year. The sewage sludges originated from the Guadalete wastewater treatment plant (WWTP) site in Jerez de la Frontera (Cádiz, Spain). These organic pollutants have been extracted from the sewage sludge by microwave energy. High performance liquid chromatography coupled with diode array (HPLC-DAD) or fluorescence (HPLC-FL) detectors have been used. The results showed that total PAHs concentration varied between 1,945 ng g(-1) dry matter (DM) for primary sludges collected in March and 10,100 ng g(-1) DM for primary sludge collected in June. Generally, concentrations of PAHs were higher in compost and digested sludge than in fresh one. On the other hand, the highest concentration of PAHs were found on summer. This thing is associated to the traffic increase from inland zones to the coast (Jerez de la Frontera is very near to beaches). Finally, this paper present a comparative study of the American an European legislation concluding that the limits of concentrations established are not exceeded. In addition heavy metals were analysed. The origin of PAHs and heavy metals seems to be different.     

低强度超声波强化剩余活性污泥好氧消化的研究

污泥是城市污水处理厂的副产物,若处理不当,将会带来一系列严重的环境问题.实验采用低强度超声波对剩余活性污泥(WAS)的好氧消化过程进行强化,选取超声强度、超声时间、超声间隔3个因素设计正交实验.结果表明,经超声辐照的WAS,其好氧消化时间最短仅约为13 d,比未经超声辐照的缩短了18.00 d.对实验结果的极差分析和方差分析表明,低强度超声波强化WAS好氧消化的最佳参数为:超声强度1.0 W/cm2、超声时间10 min、超声间隔8 h.实验还研究了WAS达标前后溶解性化学需氧量(SCOD)和总化学需氧量(TCOD)的变化情况,发现在相对较短的处理时间内,经低强度超声波强化处理的WAS的TCOD降解率仍然能与对照相近甚至高于对照,主要原因是低强度超声波强化了微生物的新陈代谢,促进了其对有机物的吸收分解.     

Inocula from activated sludge for ready biodegradability testing: homogenization by preconditioning

The use of activated sludge as inoculum source in ready biodegradability tests (RBT) suffers from several drawbacks related to the heterogeneity of these communities. In this work, the ability of a 7-day aeration period in a mineral medium to homogenize the characteristics of various activated sludges, as suggested by some RBT, was studied. The biodegradation potential of three activated sludge supernatants obtained from different wastewater treatment plants was assessed in terms of cultivable cell density, dehydrogenasic activity and a profile of hydrolytic enzymes. After the preconditioning, the homogenization of these characteristics in the supernatants was observed, as well as a decrease. When preconditioned inocula were used in acetate RBT, the biodegradation kinetics were homogenized. However, some preconditioned supernatants lost their ability to degrade an easily-assimilable xenobiotic compound (aniline) during the observation period, showing the effect of inoculum preconditioning on the behavior of complex bacterial communities, specialist populations (e.g. aniline degraders) being more sensitive than generalist populations (e.g. acetate degraders). These results show that preconditioning cannot be an optional inoculum pretreatment in RBT, and emphasize the importance of further studies focusing on inoculum homogenization.     

Effect of biopolymer on the dewatering characteristics of autothermal thermophilic aerobic digestion of sludges.

Autothermal thermophilic aerobic digestion of sludge is known to produce poorly dewatering sludges. Laboratory studies were conducted to investigate the reasons for the poor dewatering. It was found that, during digestion, proteins and polysaccharides were released into solution, and that these could be linked to the deterioration in dewatering. The biopolymer release was accompanied by an increase in the monovalent-to-divalent (M/D) cation ratio. The degree to which the M/D caused deterioration of the sludges depended on the presence of iron in sludge. When the iron content was high, the release of protein and polysaccharides was low. When iron was low, the release of protein and polysaccharides increased linearly with the M/D ratio. The dose of conditioning chemicals, cationic polymer or ferric chloride, was related to the amount of colloidal biopolymer present in solution. The findings suggest that the addition of iron during the digestion process has the potential to produce better dewatering sludges.     

Changes in sewage sludge carbon forms along a treatment stream

The behaviour and fate of macronutrients and pollutants in sewage sludge applied to the land are affected by the chemical composition of the sludge organic matter, which in turn is influenced by both sewage source and by sewage treatment processes. In this study, (13)C nuclear magnetic resonance (NMR) spectroscopy was used to characterise the organic matter of sludges collected at three different points along the treatment stream of a municipal sewage works with a domestic catchment. Sludge at the first point, an undigested liquid (UL) sludge, had a substantially different composition to the anaerobically digested (AD) and dewatered sludge cake (DC) materials, which were similar to each other. In particular, the UL sludge contained more alkyl C than the AD or DC sludges. All three sludges were found to contain mobile alkyl C that is poorly observed using the cross polarisation (CP) technique, necessitating the use of the less sensitive, but more quantitatively reliable direct polarisation (DP) technique to obtain accurate distributions of C types.     

污水污泥有机调质浓缩和无机调质脱水工艺研究

介绍了一种污水污泥有机调质浓缩和无机调质脱水工艺,它可有效提高污泥浓缩和脱水效率。含水率99％以上的剩余污泥经过有机调质后可快速浓缩至含水率93％左右,去除污泥中的间隙水和表面吸附水。浓缩污泥经过无机调质后可板框压滤脱水至含水率60％左右,脱除污泥中的毛细结合水和部分细胞水,而且实现了污泥重金属的稳定化。     

Ecotoxicity, phytotoxicity and extractability of heavy metals from different stabilised sewage sludges

The presence of heavy metals in the sludges produced in wastewater treatment plants restricts their use for agricultural purposes. This study compares different types of sludges (aerobic, anaerobic, unstabilised and sludge from a waste stabilisation pond) in order to assess the extractability of heavy metals using simple extraction, water and DTPA. The stabilisation treatment undergone by the sludges influenced the heavy metals extractability. The least mineralised sludges (unstabilised and aerobic) showed higher metal extractability. The sewage sludges were subjected to chemical characterisation and toxicity testing (ecotoxicity and phytotoxicity assays) in absence of substrate, to provide a preliminary assessment of their suitability for land application. The ecotoxicity assays confirmed that no sludge constituted a hazardous waste. The sludge extracts had significant adverse effect on the germination index (GI) of barley (Hordeum vulgare L.) and cress (Lepidium sativum L.), a fact which indicates that some characteristics affected root growth.     

Effect of humification processes on polyaromatic hydrocarbons concentration during wastewater treatment.

The aim of the present work was to compare the concentration changes of polyaromatic hydrocarbons (PAH) and the course of humification processes during wastewater treatment. Studies of samples from a biological-mechanical wastewater treatment plant in Sosnowiec-Zagórze (Poland) were carried out. Determination of PAH was performed both for wastewater sludge and sludge water. Observations of the course of humification processes for humic acid fractions isolated from sludges were conducted. Analysis of PAH extracted from wastewaters and from sludge was performed by means of high-performance liquid chromatography. Investigations of humification processes were conducted by electron paramagnetic resonance and nuclear magnetic resonance methods. The elementary composition changes in the structure of the extracted humic acids were determined. It was found that polyaromatic hydrocarbons appear during the processes of humification. Their content in water decreased only after the process of sludge aeration; however, sludge water leaving the settlers was PAH-enriched.     

Effects of long-term soil amendment with sewage sludges on soil humic acid thermal and molecular properties

Sewage sludges are frequently used as soil amendments due to their high contents of organic matter and nutrients, particularly N and P. However, their effects upon the chemistry of soil humic acids, one of the main components of the soil organic matter, need to be more deeply studied in order to understand the relation between organic matter structure and beneficial soil properties. Two sewage sludges subjected to different types of pre-treatment (composted and thermally dried) with very different chemical compositions were applied for three consecutive years to an agricultural soil under long-term field study. Thermal analysis (TG–DTG–DTA) and solid-state ¹³C NMR spectroscopy were used to compare molecular and structural properties of humic acids isolated from sewage sludges, and to determine changes in amended soils. Thermally dried sewage sludge humic acids showed an important presence of alkyl and O/N-alkyl compounds (70%) while composted sludge humic acids comprised 50% aromatic and carbonyl carbon. In spite of important differences in the initial chemical and thermal properties of the two types of sewage sludges, the chemical and thermal properties of the soil humic acids were quite similar to one another after 3 years of amendment. Long-term application of both sewage sludges resulted in 80–90% enrichment in alkyl carbon and organic nitrogen contents of the soil humic acid fraction.     

Effects of long-term soil amendment with sewage sludges on soil humic acid thermal and molecular properties

Sewage sludges are frequently used as soil amendments due to their high contents of organic matter and nutrients, particularly N and P. However, their effects upon the chemistry of soil humic acids, one of the main components of the soil organic matter, need to be more deeply studied in order to understand the relation between organic matter structure and beneficial soil properties. Two sewage sludges subjected to different types of pre-treatment (composted and thermally dried) with very different chemical compositions were applied for three consecutive years to an agricultural soil under long-term field study. Thermal analysis (TG–DTG–DTA) and solid-state ¹³C NMR spectroscopy were used to compare molecular and structural properties of humic acids isolated from sewage sludges, and to determine changes in amended soils. Thermally dried sewage sludge humic acids showed an important presence of alkyl and O/N-alkyl compounds (70%) while composted sludge humic acids comprised 50% aromatic and carbonyl carbon. In spite of important differences in the initial chemical and thermal properties of the two types of sewage sludges, the chemical and thermal properties of the soil humic acids were quite similar to one another after 3 years of amendment. Long-term application of both sewage sludges resulted in 80–90% enrichment in alkyl carbon and organic nitrogen contents of the soil humic acid fraction.     

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.     

Recovery of polyhydroxyalkanoate from activated sludge in an enhanced biological phosphorus removal bench-scale reactor.

A sequencing batch reactor was used to study the possibility of harvesting polyhydroxyalkanoate (PHA) from enhanced biological phosphorus removal (EBPR) processes without compromising treatment quality. Because, in EBPR, the highest PHA concentrations are observed after exposure of the sludge to anaerobic conditions, PHA accumulation was evaluated with collection of waste activated sludge (WAS) at the end of the anaerobic stage, in addition to the traditional removal after the aerobic stage. The system achieved good phosphorus removal, regardless of the point of WAS collection. When sludge was harvested at the end of the anaerobic stage, the PHA content of the sludge ranged from 7 to 16 mg PHA/100 mg mixed liquor volatile suspended solids. Although this level of PHA production is below levels obtained with pure cultures, the demonstrated ability to harvest PHA, while simultaneously satisfying phosphorus removal in an EBPR process, is a key initial step towards of the use of wastewater treatment plants for PHA production.     

Applications of the deep-shaft activated sludge process in wastewater treatment

The deep-shaft activated sludge process is a unique modification of the activated sludge system. The main objective of this system is to increase the amount of dissolved oxygen available for biological activity. This can be achieved by increasing the rate of oxygen transfer from the gas phase to the liquid phase. The deep-shaft configuration increases the partial pressure of oxygen, thereby causing a high saturation concentration in the reactor. In the deep-shaft process, owing to high oxygen availability, a higher organic loading can be accommodated with a comparatively low air supply. This reduces the energy and area requirements and lowers the overall cost of treatment. This technology has been successfully applied for the high-rate treatment of strongly polluted wastewater, as well as for the treatment of wastewater containing toxic or slowly biodegradable pollutants. This paper presents different applications of the deep-shaft activated sludge process, along with their relative performances.     

Utilization of urban sewage sludge: Chinese perspectives

Purpose

Urbanization and industrialization in China has resulted in a dramatic increase in the volume of wastewater and sewage sludge produced from wastewater treatment plants. Problems associated with sewage sludge have attracted increasing attention from the public and urban planners. How to manage sludge in an economically and environmentally acceptable manner is one of the critical issues that modern societies are facing.

Methods

Sludge treatment systems consist of thickening, dewatering, and several different alternative main treatments (anaerobic digestion, aerobic digestion, drying, composting, and incineration). Agricultural application, landfill, and incineration are the principal disposal methods for sewage sludge in China. However, sewage sludge disposal in the future should focus on resource recovery, reducing environmental impacts and saving economic costs.

Results

The reuse of biosolids in all scenarios can be environmentally beneficial and cost-effective. Anaerobic digestion followed by land application is the preferable options due to low economic and energy costs and material reuse.

Conclusion

It is necessary to formulate a standard suitable for the utilization of sewage sludge in China.     

微量金属对废水厌氧处理效果的影响

以葡萄酒蒸馏废水的厌氧生物处理为例,研究了Fe、Ni、Co、Mo、Cu、Zn对厌氧反应器的COD去除率、出水中挥发性有机酸含量、气体产量、气体成分、pH缓冲能力和碱度等的影响.对比了微量金属投加前后,厌氧反应器污泥中微量金属含量的变化.得出微量金属具有提高厌氧运行效果的作用,其中,Co的作用要更大一些.Ni、Co、Mo在附着态、悬浮态污泥中具有逐渐积累的特点;Fe、Cu、Zn在附着态污泥中是淋失的,而在悬浮态污泥中变化不大.     

基于CFD的污泥脱水机房恶臭扩散分布规律研究

污泥脱水机房是污水处理厂恶臭污染最严重的处理单元之一,其恶臭污染危害工作人员和周边居民身体健康。为研究脱水机房恶臭扩散分布规律,运用计算流体动力学（computational fluid dynamics, CFD）理论并采用其商用软件FLUENT对脱水机房主要恶臭污染物之一的硫化氢扩散分布进行数值模拟。案例研究了3种典型情景下的硫化氢扩散分布。结果表明,不同通风条件对脱水机房硫化氢扩散分布影响较大。在进行脱水机房设计时,应将脱水机布置于夏季最多风向的下方向,并靠近排风口,使恶臭污染物在最短的路径上排除出去,还应考虑机房其他布置,使工作人员经常接触和经过的地方位于低浓度区。