Operating aerobic wastewater treatment at very short sludge ages enables treatment and energy recovery through anaerobic sludge digestion

Conventional abattoir wastewater treatment processes for carbon and nutrient removal are typically designed and operated with a long sludge retention time (SRT) of 10–20 days, with a relatively high energy demand and physical footprint. The process also generates a considerable amount of waste activated sludge that is not easily degradable due to the long SRT. In this study, an innovative high-rate sequencing batch reactor (SBR) based wastewater treatment process with short SRT and hydraulic retention time (HRT) is developed and characterised. The high-rate SBR process was shown to be most effective with SRT of 2–3 days and HRT of 0.5–1 day, achieving >80% reduction in chemical oxygen demand (COD) and phosphorus and approximately 55% nitrogen removal. A majority of carbon removal (70–80%) was achieved by biomass assimilation and/or accumulation, rather than oxidation. Anaerobic degradability of the sludge generated in the high-rate SBR process was strongly linked to SRT, with measured degradability extent being 85% (2 days SRT), 73% (3 days), and 63% (4 days), but it was not influenced by digestion temperature. However, the rate of degradation for 3 and 4 days SRT sludge was increased by 45% at thermophilic conditions compared to mesophilic conditions. Overall, the treatment process provides a very compact and energy efficient treatment option for highly degradable wastewaters such as meat and food processing, with a substantial space reduction by using smaller reactors and a considerable net energy output through the reduced aerobic oxidation and concurrent increased methane production potential through the efficient sludge digestion.     

氧化沟处理城市污水探讨

结合实际工程,对氧化沟污水处理方法进行了深入探讨,进一步提出了寒冷地区进行氧化沟污水处理应注意的问题,以推广氧化沟处理技术的应用,促进我国城市污水处理的发展。     

深沟型氧化沟工艺在污水厂中的应用及运行分析

深沟型氧化沟工艺是在保留传统卡鲁塞尔(Carrousel)氧化沟工艺有机物去除率高、脱氮除磷效果好的基础上,将氧化沟的有效水深从4 m增加到6 m,解决了传统氧化沟占地面积大的问题;并且通过一系列设备调整,改变了传统卡鲁塞尔氧化沟的表面机械曝气装置在不同的水量和水质条件下出现搅拌能力及供氧不足的局限。最终污水处理厂出水水质均能达到GB 18918—2002《城镇污水处理厂污染物排放标准》一级B类标准。     

Combined aerobic heterotrophic oxidation, nitrification and denitrification in a permeable-support biofilm

A biofilm reactor, termed the permeable-support biofilm (PSB), was developed in which oxygen was supplied to the interior of the biofilm through a permeable membrane. The reactor was tested on filtered sewage supplemented with nutrient broth; the bulk solution was anoxic and the interior of the biofilm was supplied with pure oxygen. All tests were performed on a non-steady state biofilm with a depth of 1 mm. Mass balances on total organic carbon, ammonia, organic nitrogen and nitrate showed that combined heterotrophic oxidation of organics, denitrification and nitrification occurred simultaneously within the biofilm. The advantages of such a reactor are discussed.     

Operating a High-Rate Digester: The Southern Water Experience

Southern Water has implemented a large capital-investment programme in order to meet the requirements of the EU Urban Wastewater Treatment Directive. Within Southern Water, the Directive will result in a doubling in the quantity of wastewater sludge to be treated. In order to minimise the amount of sludge to be transported and produce a stabilised sludge which is suitable for recycling to agricultural land, the company's sludge strategy is based on treatment by mesophilic anaerobic digestion.
This paper (a) highlights some of the consequences of operating a high-rate digestion plant, and (b) focuses on areas such as depositions in thickened sludge digester feed lines, the start-up procedures for high-rate digesters, foaming, hair and fibre build-up problems and treatment failure caused by toxicity inhibition. All these problems have been corrected or controlled and have resulted in Southern Water revising and updating its design manuals and standards, to prevent such future difficulties.     

Impact of rotifer grazing on population dynamics of green microalgae in high-rate ponds

In high-rate algal ponds, the grazing activity of rotifers such as Brachionus rubens or B. calyciflorus often leads to a replacement of Scenedesmus species by Micractinium pusillum. In contrast to many other green microalgae including Scenedesmus, Micractinium pusillum with fully developed spines (setae) cannot be eaten by Brachionus. Ecological conditions for population shifts between Scenedesmus and Micractinium are, therefore, interpreted as a response of the rotifers rather than being due to physiological properties of the algae. Another effect of rotifer grazing on the microbial flora of high-rate ponds is the development of large stable flocs consisting of bacteria and microalgae.     

Floating Filters for Particle Removal in Sewage Treatment

This paper describes experiments which were carried out on a high-rate secondary-treatment plant which incorporate a moving-bed biofilm and floating filter. The same cylindrically shaped plastic elements were used both as a biofilm carrier and as a filter medium in the floating filter.     

Characterization of micron-size flyash particles by X-ray photoelection spectroscopy (ESCA)

X-ray photoelectron spectroscopy has been used to identify and determine the concentrations and oxidation states for a number of major and minor elements present on the surface of micron-size fly-ash particles. Relative concentrations as a function of depth were obtained for Si, Al, Ti, Fe, Ca, Na, C, O, and S using a sputter-etching procedure. The concentrations of Na, C, and S were found to decrease, and Si, Al, Fe, and Ca were found to increase to a depth of approximately 500 Å. Analysis of a larger size fraction gave depth profiles which were similar to those from micron-size particles. The results are discussed in terms of current models for the formation of fly ash.     

Changes in arsenic speciation through a contaminated soil profile: a XAS based study

An impacted soil located near an industrial waste site in the Massif Central near Auzon, France, where arsenical pesticides were manufactured, has been studied in order to determine the speciation (chemical forms) of arsenic as a function of soil depth. Bulk As concentrations range from 8780 mg kg(-1) in the topsoil horizon to 150 mg kg(-1) at 60 cm depth. As ores (orpiment As2S3, realgar AsS, arsenopyrite FeAsS) and former Pb- and Al-arsenate pesticides have been identified by XRD at the site and are suspected to be the sources of As contamination for this soil. As speciation was found to vary with depth, based on XRD, SEM-EDS, EPMA measurements and selective chemical extractions. Based on oxalate extraction, As is mainly associated with amorphous Fe oxides through the soil profile, except in the topsoil horizons where As is hosted by another phase. SEM-EDS and EPMA analyses led to the identification of arseniosiderite (Ca2Fe3+3(AsVO4)3O2.3H2O), a secondary mineral that forms upon oxidation of primary As-bearing minerals like arsenopyrite, in these topsoil horizons. These mineralogical and chemical results were confirmed by synchrotron-based X-ray absorption spectroscopy. XANES spectra of soil samples indicate that As occurs exclusively as As(V), and EXAFS results yield direct evidence of changes in As speciation with depth. Linear combination fits of EXAFS spectra of soil samples with those of various model compounds indicate that As occurs mainly As-bearing Fe(III)-(hydr)oxides (65%) and arseniosiderite (35%) in the topsoil horizon (0-5 cm depth). Similar analyses also revealed that there is very little arseniosiderite below 15 cm depth and that As(V) is associated primarily with amorphous Fe oxides below this depth. This vertical change of As speciation likely reflects a series of chemical reactions downward in the soil profile. Arseniosiderite, formed most likely by oxidation of arsenopyrite, is progressively dissolved and replaced by less soluble As-bearing poorly ordered Fe oxides, which are the main hosts for As in well aerated soils.     

Interstitial inorganic phosphorus concentrations in lakes Mendota and Wingra

Interstitial P levels in Lake Mendota and Lake Wingra were evaluated as a function of season and water column and sediment depth. Interstitial water was obtained by the centrifugation-filtration method. Temporal variations were observed over the entire 15 cm sediment depth interval examined in all four locations evaluated. Interstitial reactive P (IRP) levels in Lake Mendota ranged from 0.014–1.67 mg l⁻¹ at the 5–6 m water column depth and from 1.20–5.75 mg l⁻¹ at the 18–19.5 m depth. IRP levels in Lake Wingra ranged from 0.029–2.15 mg l⁻¹ at 3.5 m and from 0.191–3.96 mg l⁻¹ at 2 m. Variations in interstitial P were attributed to variations in oxidation state of Fe as influenced by oxygen transport and reduction rates.     

Operation of high-rate oxidation ponds: theory and experiments

Optimal operation of high rate oxidation ponds depends mainly on the climatic conditions of the pond's location. The major factors affecting pond performance are solar radiation and water temperature, the former determines mainly maximal algal productivity while the latter determines optimal retention time operation. Pond dimensions, namely area and depth, are the only true independent variables which can be manipulated to produce optimal retention time in year-round operation. In the tropical regions a constant retention time is most adequate for optimal operation as water temperature is fairly constant year-round and a constant area and depth strategy can be adopted. In moderate climates seasonally variable retention time is preferred and it was found to be best economically achieved by varying pond depth at constant area. Another plausible strategy with possible economic advantages is a combination of dual function ponds operating solely for wastewater treatment during winter while some are converted into fish-rearing ponds during summer.     

Biological oxidation and disinfection of sludge

Aerobic digestion, which is biological oxidation of sludge, produces heat. Enough heat is liberated to raise the temperature of the wet sludge up to the pasteurizing range (60–70°C). The major heat loss from an aerobic digester is the latent heat of vaporization of the water vapor which is carried of in the waste air. The use of concentrated oxygen to replace air minimizes this heat loss and theoretically permits thermophilic operation if the initial sludge solids are greater than about 4 per cent. Pilot scale studies have shown that thermophilic aerobic digestion is practical and can be carried out in less than 24 h. Capital and operating costs are reduced and the sludge is pasteurized without the use of external heat. The process is a form of high-rate wet composting and produces a sludge ideally suited for disposal on agricultural lands.Recent and current research data from U.S. EPA-sponsored studies on aerobic digestion of primary sludge solids at Hollywood, Florida; mixed primary and waste activated sludge solids at Hamilton, Ohio; and waste activated sludge solids at Denver, Colorado, are presented and critiqued in light of present design methodology and constraints. These data were obtained under a variety of operating conditions. Data and discussion are also given on the use of pure oxygen in digestion of thickened waste activated sludges.     

Sequential extraction of sulfide-rich tailings remediated by the application of till cover,Kristineberg mine,northern Sweden

A sequential extraction has been carried out on sulfide-rich mine tailings. The purpose was to investigate how elements released by oxidation are secondarily retained in the tailings and the possible consequences of the remediation. After investigating the solid tailings, seven samples were chosen for sequential extractions. Two samples were oxidised, situated just above the oxidation front; two samples from just below the former oxidation front with increased concentrations of several elements; two unoxidised samples were from an intermediate depth, and the deepest sample was from the tailings-peat boundary at the bottom of the impoundment. Five phases were extracted: adsorbed/exchangeable/carbonate; labile organics; amorphous Fe-oxyhydroxides/Mn-oxides; crystalline Fe-oxides; and organics/sulfides. The addition from dried porewater to the extracted fractions has been calculated and considered as minor. In the oxidised tailings, the sulfide fraction still dominates for elements such as Fe, S, Cd, Co, Cu, Hg and Zn, although the concentrations are low compared to the unoxidised tailings. Generally, the second most important fraction is the adsorbed/exchangeable/carbonate fraction. Below the oxidation front, the sulfide content of the tailings sharply increases. In the secondary enrichment zone, the total element concentrations increase compared with the deeper unoxidised samples, mainly due to secondary retention. For some elements, secondary retention is greater than the total amount extracted for the deeper unoxidised samples. In the secondary enrichment zone the adsorbed/exchangeable/carbonate fraction represents approximately 20 wt.% or more for Cd, Co, Mn, Ni and Zn. The amorphous iron oxyhydroxide or the crystalline iron oxide fractions are less important at this level, although for As, Ba and Cu the amorphous iron oxyhydroxide fraction represents up to 20 wt.%. At the lower border of the enrichment zone, the total concentration for most metals is lower, but the importance of the adsorbed/exchangeable/carbonate fraction is further enhanced for Cd, Cu, Ni and Zn. These elements have 35-60 wt.% of the total amount from this fraction. For As, Cd, Cu, Ni and Pb, the secondary fractions extracted (extractions A-D) represent between 60 and 80 wt.% of the total content. At greater depth in the impoundment the relative importance of the adsorbed/exchangeable/carbonate fraction decreases, whilst the importance of amorphous iron oxyhydroxide and crystalline iron oxide fractions increases. The adsorbed/exchangeable/carbonate fraction is the most easily remobilised fraction. A raised groundwater table previously situated below the enrichment zone may result in the release of secondarily retained metals.     

Alum clarification for improving wastewater effluent quality

This paper presents results of an investigation on the application of alum for improving the overall performance of wastewater treatment plants. These studies were conducted on a pilot scale of 7200 gal day⁻¹. The pilot plant incorporated parallel systems for evaluating conventional and high-rate clarification. The conventional system included chemical addition, rapid mix, flocculation, sedimentation, and rapid sand filtration. The high-rate system differed in that the flocculated solids were introduced directly onto a dual-media filter with no intermediate sedimentation.Results of this study indicate that in both types of tertiary clarification treatment, greater than 95 per cent removal of the BOD of a nitrified secondary effluent, turbidity, and suspended solids were achieved with alum doses of 40–60 mg 1⁻¹. Efficient phosphorus removals were also realized in the same systems by increasing the alum dose to about 150 mg 1⁻¹. In addition to the removal of BOD and phosphorus, bacteria and heavy metals were removed.     

Biodegradability and change of physical characteristics of particles during anaerobic digestion of domestic sewage

At the high-rate anaerobic treatment of domestic sewage, both biological and physical processes play an important role. Therefore, the anaerobic biodegradability of raw, paper-filtered and membrane-filtered sewage and black water has been investigated in batch experiments. Additionally, the effect of anaerobic digestion on physical characteristics, like particle size, surface tension and zeta-potential, of the present particles is studied. The biodegradability of domestic sewage and black water at 30 degrees C is almost similar (71-74%). Moreover, a high methanogenesis of the colloidal fraction in domestic sewage (86 +/- 3%) is achieved, showing that the low removal of colloidal particles in continuous high-rate anaerobic reactors is due to low physical removal rather than biodegradability. The lowest biodegradability is demonstrated for the dissolved fraction (62%). The results show that after anaerobic digestion the average radius of particles with diameter < 4.4 and < 0.45 microns increased for domestic sewage, while it decreased for black water. Part of the surface-active components in domestic sewage is not biodegraded during anaerobic batch digestion, as indicated by the development of the surface tension. The negative zeta-potential of all particles hardly changes during digestion, showing that colloidal interactions were not affected by anaerobic digestion.     

沉淀/高速气浮联用技术用于给水厂改造

为了解决由于高藻水源水引发的产水量下降、滤池反冲洗周期缩短、出水余铝超标、投药量大幅增加以及出水嗅味严重等问题,采用沉淀/高速气浮联用技术对水厂的平流沉淀池进行改造(不增加占地),并加设静态混合器,改善絮凝剂的混合效果.改造后的运行结果表明,出水水质完全满足国家饮用水卫生标准,高藻暴发期间投药量仅为改造前的1/3.     

Computational study of flow characteristics of acid mine drainage on the structure of oxidation pond

A computational flow analysis using the concept of the inflow age was conducted to evaluate the flow characteristics and retention time depending on the shape and number of inlets and outlets in an oxidation pond. The oxidation pond was rectangular in shape with a width‐to‐length ratio of 3, a depth of 3 m, an area of 500 m², and square‐shaped inlet and outlet. The flow rate of the mine drainage was set to 5 L/s. The computational flow analysis showed that the homogeneity and inflow exchange efficiency were the highest when the width‐to‐height ratio of the inlet and outlet was 0.5, while they were the lowest when it was 1.0. The number of inlets in the oxidation pond had a significant effect on the flow characteristics in the pond, whereas the number of outlets had no significant effect. The homogeneity and inflow exchange efficiency appeared to be the highest when the number of inlets was two.     

A dynamic model of the high-rate algal-bacterial wastewater treatment pond

A mathematical model is presented to describe the symbiotic growth of algae and bacteria in a high-rate wastewater treatment pond. Good agreement with available experimental results is demonstrated. The variation of process parameters (pH, DO and substrate concentration) with channel length and time of day is illustrated for a recirculated pond of “race-track” design. The influence of operating conditions on the algal yield obtainable is evaluated.     

Enhanced nitrogen removal from pharmaceutical wastewater using SBA-ANAMMOX process

Efficient biological nitrogen removal from pharmaceutical wastewater has been focused recently. The present study dealt with the treatment of colistin sulfate and kitasamycin manufacturing wastewater through anaerobic ammonium oxidation (ANAMMOX). The biotoxicity assay on luminescent bacterium Photobacterium phosphoreum (T3 mutation) showed that the pharmaceutical wastewater imparted severe toxicity with a relative luminosity of 3.46% ± 0.45%. During long-term operation, the cumulative toxicity from toxic pollutants in wastewater resulted in the performance collapse of conventional ANAMMOX process. A novel ANAMMOX process with sequential biocatalyst (ANAMMOX granules) addition (SBA-ANAMMOX process) was developed by combining high-rate ANAMMOX reactor with sequential biocatalyst addition (SBA). At biocatalyst addition rate of 0.025 g VSS (L wastewater)⁻¹ day⁻¹, the nitrogen removal rate of the process reached up to 9.4 kg N m⁻³ day⁻¹ in pharmaceutical wastewater treatment. The effluent ammonium concentration was lower than 50 mg N L⁻¹, which met the Discharge Standard of Water Pollutants for Pharmaceutical Industry in China (GB 21903-2008). The application of SBA-ANAMMOX process in refractory ammonium-rich wastewater is promising.     

Nitrogenous compounds in facultative oxidation pond sediments

The protein content of sludge samples from facultative oxidation ponds was measured and was found to have even distribution in the pond floor. Proteolytic activity which degrades protein to intermediate compounds, was found to be slightly higher near the pond inlet region. It was also shown that proteolytic activity increased with increasing depth of overlying pond liquor.Ammonia content of, and ammonification by pond sludge appeared to be independent of locality. Urea and urease activity were restricted to the regions close to the pond inlet region.