Phosphorus removal by sands for use as media in subsurface flow constructed reed beds

Sorption of P to the bed sand medium is a major removal mechanism for P in subsurface flow constructed reed beds. Selecting a sand medium with a high P-sorption capacity is therefore important to obtain a sustained P-removal. The objective of this study was to evaluate the P-removal capacities of 13 Danish sands and to relate the removal to their physico-chemical characteristics. The P-removal properties were evaluated in short-term isotherm batch-experiments as well as in 12-week percolation experiments mimicking the P-loading conditions in constructed reed bed systems. The P-removal properties of sands of different geographical origin varied considerably and the suitability of the sands for use as media in constructed reed beds thus differs. The P-removal capacity of some sands would be used up after only a few months in full-scale systems, whereas that of others would persist for a much longer time. The most important characteristic of the sands determining their P-removal capacity was their Ca-content. A high Ca content favours precipitation with P as sparingly soluble calcium phosphates particularly at the slightly alkaline conditions typical of domestic sewage. In situations where the wastewater to be treated is more acid, the contents of Fe and Al may be more important as the precipitation reactions with these ions are favoured at lower pH levels. The maximum P-sorption capacities estimated using the Langmuir-isotherm plots did not correspond to or correlate with the actual amount of P removed in the percolation columns. Hence, the Langmuir-isotherm does not estimate the P-removal capacities of sands. It is suggested that a suitable quick method of screening a selection of potential media for P-removal potential is to perform simple removal isotherm studies using water with a similar chemical composition as the wastewater to be treated. This method will not provide a direct estimate of the P-removal capacity that can be obtained in full-scale systems, but it is a means of comparing the relative performance of potential media.     

无锡主城区污水厂升级改造脱氮除磷与污泥产量分析

无锡主城区三大污水处理厂分别采用不同的污水处理工艺,在升级改造过程中分别根据进水水质条件及处理工艺运行特点,对工程设计及运行参数进行了调整。以这三大污水处理厂升级改造前、后实际运行数据为依据,着重分析了其脱氮除磷工艺改造、实际运行效果及由此引起的污泥产量变化。     

The influence of nitrilotriacetic acid on heavy metal transfer in the activated sludge process-I. at constant loading

Removal of metals in the sewage treatment process is closely related to the chemical forms in which the metals exist. One critical factor controlling the forms of the metals in sewage is the chemical matrix of the sewage; as a consequence of their chelating capacity detergent builders are important in modifying the sewage matrix. Laboratory simulations of the activated sludge process have been studied to estimate the impact of the detergent builder nitrilotriacetic acid on the removal of heavy metals from sewage in this treatment process.The acclimation period for the biodegradation of nitrilotriacetic acid in a hard water synthetic sewage was found to vary from 16 to 31 days. In a soft water synthetic sewage, biodegradation was not observed even after 60 days. Hydrolysis of condensed phosphates in both hard and soft water synthetic sewages occurred within 3 h. Even when substantially biodegraded in hard water synthetic sewage, nitrilotriacetic acid appeared to be adversely affected by the absorption of cadmium, copper and zinc by the biological solids. The greatest absorption of heavy metals to the biological solids occurred when condensed phosphates were present. In soft water synthetic sewage metal absorption was minimal in the presence of nitrilotriacetic acid. In the presence of condensed phosphates absorption was considerably higher but not comparable with that achieved in hard water synthetic sewage.     

Fecal coliform removal in wastewater treatment plants studied by plate counts and enzymatic methods

Twelve wastewater treatment plants (WWTPs) were sampled in France and Belgium in 1999 and 2000 in order to estimate the fecal coliform (FC) removal efficiency of various types of treatment. Only one of these WWTPs was equipped with a specific step to eliminate microorganisms (UV disinfection preceded by sand filtration). FC abundance was measured in raw and treated sewage by plate counts on selective medium and rapid beta-D-glucuronidase (GLUase)-based assays. Removal of culturable FC was the most efficient in treatments with high retention time (activated sludge process with nitrification and denitrification, lagooning), in biofiltration and in the treatment with a tertiary disinfection step. GLUase activity measurements showed the same removal pattern as plate counts except for UV disinfection, where no reduction of GLUase activity was measured. Specific loads of culturable FC and GLUase activity, i.e. daily amounts of culturable FC or GLUase activity in sewage per inhabitant-equivalent, were calculated in raw and treated wastewater for the different WWTPs.     

Evaluation of the fate of perfluoroalkyl compounds in wastewater treatment plants

Recent studies have shown that the wastewater treatment plant (WWTP) is a significant source of perfluoroalkyl compounds (PFCs) in natural water. In this study, 10 PFCs were analyzed in influent and effluent wastewater and sludge samples in 15 municipal, 4 livestock and 3 industrial WWTPs in Korea. The observed distribution pattern of PFCs differed between the wastewater and sludge samples. Perfluorooctane sulfonate (PFOS) was dominant in the sludge samples with a concentration ranging from 3.3 to 54.1 ng/g, whereas perfluorooctanoic acid (PFOA) was dominant in wastewater and ranged from 2.3 to 615 ng/L and 3.4 to 591 ng/L in influent and effluent wastewater, respectively. Principal component analysis (PCA) results provided an explanation for this variation in PFC distribution patterns in the aqueous and sludge samples. The fates of PFCs in the WWTPs were related with the functional groups. The PFOS concentrations tended to decrease after treatment in most WWTPs, whereas PFOA increased. The different fates of PFOA and PFOS in WWTPs were attributed to the higher organic carbon-normalized distribution coefficient of perfluoroalkylsulfonate (PFASs) than that of the carboxylate analog, indicating the preference of PFASs to partition to sludge. Although industrial WWTPs contained high concentration of PFCs, they are not the main source of PFCs in Korean water environment because of their small release amount. WWTPs located in big cities discharged more PFCs, suggesting household sewage is one of the significant sources of PFCs contamination in the environment.     

Minimization of excess sludge production for biological wastewater treatment

Excess sludge treatment and disposal currently represents a rising challenge for wastewater treatment plants (WWTPs) due to economic, environmental and regulation factors. There is therefore considerable impetus to explore and develop strategies and technologies for reducing excess sludge production in biological wastewater treatment processes. This paper reviews current strategies for reducing sludge production based on these mechanisms: lysis-cryptic growth, uncoupling metabolism, maintenance metabolism, and predation on bacteria. The strategies for sludge reduction should be evaluated and chosen for practical application using costs analysis and assessment of environmental impact. High costs still limit technologies of sludge ozonation-cryptic growth and membrane bioreactor from spreading application in full-scale WWTPs. Bioacclimation and harmful to environment are major bottlenecks for chemical uncoupler in practical application. Sludge reduction induced by oligochaetes may present a cost-effective way for WWTPs if unstable worm growth is solved. Employing any strategy for reducing sludge production may have an impact on microbial community in biological wastewater treatment processes. This impact may influence the sludge characteristics and the quality of effluent.     

Polybrominated diphenyl ethers in sewage sludge and treated biosolids: Effect factors and mass balance

Polybrominated diphenyl ether (PBDE) flame retardants have been consistently detected in sewage sludge and treated biosolids. Two hundred and eighty-eight samples including primary sludge (PS), waste biological sludge (WBS) and treated biosolids from fifteen wastewater treatment plants (WWTPs) in Canada were analyzed to investigate the factors affecting accumulation of PBDEs in sludge and biosolids. Factors examined included environmental/sewershed conditions and operational parameters of the WWTPs. PBDE concentrations in PS, WBS and treated biosolids were 230–82,000 ng/g, 530–8800 ng/g and 420–6000 ng/g, respectively; BDE-209,-99, and -47 were the predominant congeners. Concentrations were influenced by industrial input, leachate, and temperature. Several examinations including the measurement of BDE-202 indicated minimal debromination during wastewater treatment. Estimated solids-liquid distribution coefficients were moderately correlated to hydraulic retention time, solids loading rate, mixed liquor suspended solids, solids retention time, and removal of organic solids, indicating that PBDE partitioning to solids can be optimized by WWTPs' operational conditions. Solids treatment type strongly affected PBDE levels in biosolids: 1.5 times increase after solids digestion, therefore, digestion efficiency could be a potential factor for variability of PBDEs concentration. In contrast, alkaline treatment reduced PBDE concentrations in biosolids. Overall, mass balance approaches confirmed that PBDEs were removed from the liquid stream through partitioning to solids. Variability of PBDE levels in biosolids could result in different PBDEs burdens to agricultural land, and different exposure levels to soil organisms.     

Fate of nonylphenol polyethoxylates and their metabolites in four Beijing wastewater treatment plants

Four Beijing wastewater treatment plants (WWTPs) were selected to investigate behaviours of nonylphenol polyethoxylates and their metabolites in different wastewater treatment processes. The results showed that the total concentrations of nonylphenolic compounds in the influents of the four WWTPs ranged from 0.115 to 0.347 μmol/L, as well as their removal efficiencies ranging from 75.7% to 90.8%. Both influent concentrations and removal efficiencies of nonylphenol polyethoxylates were correlated to seasons as follows: higher in the summer than in the winter, and influent concentrations were lower during the rain weather. The analysis revealed that 21.8-47.6% of nonylphenol polyethoxylates and their metabolites entering WWTPs were released via effluents and excess sludge, leaving a great part of them for biodegradation. Nonylphenol and short-chain nonylphenol polyethoxylates were disposed to the environment mainly via sewage sludge, while carboxylated nonylphenol polyethoxylates were the most abundant group of nonylphenol polyethoxylates in effluents.     

Comparison of humification processes occurring during sewage purification in treatment plants with different technological processes

The course of the humification process of sewage sludge collected from three biologic-mechanical treatment plants with different treatment technologies was studied. The maturity of sewage sludge and its usefulness for agricultural purposes was also discussed. The physical-chemical properties of humic acids extracted from sewage sludge received from comparable stages of sludge purification were described. Changes of the sludge properties during sewage purification and the progress of the humification process were investigated with EPR, IR and UV/VIS spectroscopic methods. The content of the elements and the carboxylic groups in humic acids extracted from each stage of the sewage treatment were also determined. It was found that the humification processes take place in all three treatment plants but with different intensities resulting from the differences in the individual cleaning processes in these plants. The most intensive changes of physical-chemical parameters in the extracted humic acids were observed in the anaerobic digester where mesophilic fermentation occurs. The sludge oxygenation processes also significantly affect the course of the humification process during sewage treatment.     

Meeting the phosphorus consent with biological nutrient removal under UK winter conditions

It is estimated that up to 342 wastewater treatment plants (Wwtps) in England and Wales will require a phosphorus (P) consent by 2010. Although biological P removal is considered to be the most sustainable option for P removal, it has always been problematic for plants that remove both nitrogen and P due to the inadequate concentration of organic material during wet periods. Two biological nutrient removal (BNR) configurations, the Johannesburg (JHB) process and a combined JHB and five-stage Bardenpho process, were evaluated over a period of 2 years to assess the impact of sewage strength on bio-P removal. The JHB achieved an average effluent total phosphorus (TP) of 2.4 mg/L and the combined JHB and five-stage process averaged 1.4 mg/L effluent TP. The major problems affecting the performance of both configurations were: dissolved oxygen (DO) in the recycled mixed liquor, nitrate in the return activated sludge (RAS) and low influent biological oxygen demand (BOD) concentrations. Acetate dosing proved successful as a source of volatile fatty acids (VFAs) in the anaerobic zone during periods of low-strength sewage. An acetate dosing strategy based on the influent flow rate to the plant was found to be a simple and effective technique that ensured that a consent of <1 mg TP/L could be met.     

城市污水处理化学除磷药剂的应用比较

对城市污水处理过程中几种常用的化学除磷进行了比较分析,从经济角度和工程应用角度出发,得出了各种化学除磷药剂的优缺点和适用条件,并对处理系统中的活性污泥和排放水体潜在的影响和危害进行简要评价,以供污水处理人员在辅助化学除磷过程中参考。     

Occurrence, partition and removal of pharmaceuticals in sewage water and sludge during wastewater treatment

During 8 sampling campaigns carried out over a period of two years, 72 samples, including influent and effluent wastewater, and sludge samples from three conventional wastewater treatment plants (WWTPs), were analyzed to assess the occurrence and fate of 43 pharmaceutical compounds. The selected pharmaceuticals belong to different therapeutic classes, i.e. non-steroidal anti-inflammatory drugs, lipid modifying agents (fibrates and statins), psychiatric drugs (benzodiazepine derivative drugs and antiepileptics), histamine H2-receptor antagonists, antibacterials for systemic use, beta blocking agents, beta-agonists, diuretics, angiotensin converting enzyme (ACE) inhibitors and anti-diabetics. The obtained results showed the presence of 32 target compounds in wastewater influent and 29 in effluent, in concentrations ranging from low ng/L to a few μg/L (e.g. NSAIDs). The analysis of sludge samples showed that 21 pharmaceuticals accumulated in sewage sludge from all three WWTPs in concentrations up to 100 ng/g. This indicates that even good removal rates obtained in aqueous phase (i.e. comparison of influent and effluent wastewater concentrations) do not imply degradation to the same extent. For this reason, the overall removal was estimated as a sum of all the losses of a parent compound produces by different mechanisms of chemical and physical transformation, biodegradation and sorption to solid matter. The target compounds showed very different removal rates and no logical pattern in behaviour even if they belong to the same therapeutic groups. What is clear is that the elimination of most of the substances is incomplete and improvements of the wastewater treatment and subsequent treatments of the produced sludge are required to prevent the introduction of these micro-pollutants in the environment.     

Removal of bis(2-ethylhexyl) phthalate at a sewage treatment plant

Bis(2-ethylhexyl) phthalate (DEHP) concentrations were measured at different stages in a full-scale sewage treatment plant (STP) and mass balances were calculated. The DEHP load to treatment process coming from the sewer system and the internal load comprising returned supernatants and filtrate from sludge treatment and excess secondary sludge were at the same level. The DEHP removal efficiency from the water phase at the STP was on average 94% of sewage DEHP, the main removal process being sorption to primary and secondary sludges. On average 29% of DEHP was calculated to be removed in the biological nitrifying-denitrifying activated sludge process, which was much less than expected from laboratory biodegradation studies described in literature. Monoethylhexyl phthalate, the primary biotransformation product of DEHP, was not detected at any treatment stage. Approximately 32% of DEHP in sewage was removed during anaerobic digestion of the sludge, while 32% remained in the digested and dewatered sludge.     

Lightweight properties and pore structure of foamed material made from sewage sludge ash

Pore structure significantly affects the lightweight characteristics and thermal performance of materials. Therefore, in this study, sewage sludge ash (SSA) was used to make lightweight materials. Physical and chemical properties, and how the mixing proportions affected the foaming behavior were investigated, including the lightweight characteristics and pore structure of the materials produced. The experiments showed that the minimum required cement amount was determined by the compressive strength of the sewage sludge ash foamed material (SSAFM), not its alkali content. The hydration of cement and SSA mainly generated pores with diameters of less than 0.1  μm, but cement added with metallic aluminum powder produced pores with diameters larger than 10  μm. The addition of SSA increased the volume of pores smaller than 10  μm. The thermal conductivity of SSAFM was between 0.084 and 0.102 W/m K. Therefore, SSA could be used as the lightweight filler and heat-insulating material.     

Effect of season of application on the adhesion, retention and recontamination of herbage by potentially toxic metals and sewage sludge

Grassland in the United Kingdom can accept sewage sludge when, as a result of cropping restrictions, arable land cannot. However, one of the uncertainties associated with the application of sewage sludge to grassland is the potential exposure of the grazing ruminant to sewage sludge particulates adhered to the grass or deposited on the soil surface. The implications of elevated levels of sludge particulates and associated potentially toxic metals (PTMs) are the potential accumulation of PTMs into edible tissues of the grazing animal. Two experiments were performed to investigate the effect of season of application on the adhesion, retention and recontamination of herbage by sewage sludge and PTMs. In each experiment, three treatments were installed, an untreated control, application of sludge in the autumn and application of sludge in the spring. Sewage sludge particulates and PTMs were eluted sequentially 21 days after the application of sludge using water and detergent and the residual (tissue) concentrations were monitored. Total concentrations in each fraction and adhesion indices were calculated. Soil samples taken from the sward treatments after each application showed no elevated concentrations of PTMs or concentrations that approached the maximum concentrations allowed for soils amended with sewage sludge. The amounts of sludge adhered to herbage ranged from 114 to 360 g sludge DM/kg herbage DM. There was evidence of preferential retention of PTMs to herbage. However, during the 21-day no grazing period there was a general decline in concentration of all PTMs. Copper was retained on the herbage for greater periods of time compared to Zn, CD, Pb and Fe (P < 0.01). The proportion of Pb recovered from the water phase increased during the 21-day no grazing period in comparison to Cu, Zn and Fe (P < 0.001). It is concluded that the concentrations of PTMs adhered and integral to herbage as a result of surface application of sewage sludge are likely to fall to acceptable levels in well-managed permanent grassland.     

Phosphorus recovery from sewage sludge with a hybrid process of low pressure wet oxidation and nanofiltration

Phosphorus recovery from sewage sludge will become increasingly important within the next decades due to depletion of mineral phosphorus resources. In this work a new process concept was investigated, which aims at realising phosphorus recovery in a synergistic way with the overall sewage sludge treatment scheme. This process combines a low pressure wet oxidation for sewage sludge decomposition as well as phosphorus dissolution and a nanofiltration process to separate phosphorus from heavy metals and obtain a clean diluted phosphoric acid, from which phosphorus can be recovered as clean fertiliser.It was shown that this process concept is feasible for sewage sludge for wastewater treatment plants that apply enhanced biological removal or precipitation with alumina salts for phosphorus removal. The critical parameter for phosphorus dissolution in the low pressure wet oxidation process is the iron concentration, while in the nanofiltration multi-valent cations play a predominant role.In total, a phosphorus recovery of 54% was obtained for an exemplary wastewater treatment plant. Costs of the entire process are in the same range as conventional sewage sludge disposal, with the benefit being phosphorus recovery and reduced emission of greenhouse gases due to avoidance of sludge incineration.     

Biological hydrolysis and acidification of sludge under anaerobic conditions: the effect of sludge type and origin on the production and composition of volatile fatty acids

New wastewater treatment processes resulting in considerably reduced sludge production and more effective treatment are needed. This is due to the more stringent legislations controlling discharges of wastewater treatment plants (WWTPs) and existing problems such as high sludge production. In this study, the feasibility of implementing biological hydrolysis and acidification process on different types of municipal sludge was investigated by batch and semi-continuous experiments. The municipal sludge originated from six major treatment plants located in Denmark were used. The results showed that fermentation of primary sludge produced the highest amount of volatile fatty acids (VFAs) and generated significantly higher COD- and VFA-yields compared to the other sludge types regardless of which WWTP the sludge originated from. Fermentation of activated and primary sludge resulted in 1.9-5.6% and 8.1-12.6% COD-yields, soluble COD (SCOD)/total COD (TCOD), in batch experiments, respectively. The COD-yields for primary, activated and mixed sludge were 19.1%, 6.5% and 21.37%, respectively, in semi-continuous experiments operated at solids retention time (SRT) of 5d and temperature of 37 degrees C. The benefit of fermentation for full-scale application was roughly estimated based on the experiments performed in semi-continuous reactors. The results revealed that even though the VFA production of primary sludge was higher compared to activated sludge, substantial amounts of VFA could be produced by fermentation of activated sludge due to the substantially higher production of activated sludge in WWTPs.     

The solids retention time-a suitable design parameter to evaluate the capacity of wastewater treatment plants to remove micropollutants

Micropollutants as endocrine disrupting compounds (EDC) or pharmaceuticals are of increased interest in water pollution control. Wastewater treatment plant (WWTP) effluents are relevant point sources for residues of these compounds in the aquatic environment. The solids retention time (SRT) is one important parameter for the design of WWTPs, relating to growth rate of microorganisms and to effluent concentrations. If a specific substance is degraded in dependency on the SRT, a critical value for the sludge age can be determined. In WWTPs operating SRTs below this critical value, effluent concentrations in the range of influent concentrations or a distribution according to the adsorption equilibrium have to be expected, whereas in WWTPs operating at SRTs higher than the critical value degradation will occur. Critical SRTs were determined for different micropollutants, indicating that the design criteria based on the sludge age allows an estimation of emissions. Different treatment technologies as conventional activated sludge systems and a membrane bioreactor were considered and no significant differences in the treatment efficiency were detected when operated at comparable SRT. The results of the investigations lead to the conclusion that low effluent concentrations can be achieved in WWTPs operating SRTs higher than 10 days (referred to a temperature of 10 degrees C). This corresponds to the requirements for WWTPs situated in sensitive areas according to the urban wastewater directive of the European Community (91/271/EEC) in moderate climatic zones.     

Sewage sludge stabilisation with calcium hydroxide: effect on physicochemical properties and molecular composition

Raw primary sewage sludge (Wastewater Treatment Plant of Krotoszyn, SW Poland) and its mixtures with 3%d, 6%d, 9%d, 12%d and 24%d of calcium hydroxide were stabilised for 1 and 35 days. Changes of the sludge physicochemical properties and molecular composition, caused by alkaline agent in course of stabilisation process, are recognised. A basic physicochemical data on the sludge cake and filtrate after 1 and 35 days of stabilisation process are given. Soxhlet extracts from the sludge cakes stabilised for 35 days as well pyrolysis and pyrolysis in situ methylation (using tetramethylammonium hydroxide-TMAH) products of respective pre-extracted cake residues were analysed by gas chromatography-mass spectrometry (GC-MS). Increase of calcium hydroxide concentration in the sludge mixture causes enhanced ammonia release, preferential hydrolyses of fats and proteins from the sludge macromolecular network and transformation of free fatty acids contained in the sludge lipids, as well as these released hydrolytically, to their calcium salts. The sewage sludge stabilisation with calcium hydroxide has no effect on homological assemblage and content of unbound stanol and sterol compounds in the sludge lipids and these bound into macromolecular network. Biogenic n-alkanes and anthropogenic linear alkylbenzenes were detected as minor components in the lipids and pyrolytic products from the pre-extracted cake residue, respectively. The alkaline agent used for the sludge stabilisation accelerates equilibration of the process and reduces content of pathogenic microorganisms.     

Occurrence and removal of antibiotics, hormones and several other pharmaceuticals in wastewater treatment plants of the largest industrial city of Korea

Occurrence and removal efficiencies of 20 pharmaceuticals and personal care products (PPCPs) including antibiotics, hormones, and several other miscellaneous pharmaceuticals (analgesics, antiepileptics, antilipidemics, antihypertensives, antiseptics, and stimulants) were investigated in five wastewater treatment plants (WWTPs) of Ulsan, the largest industrial city of Korea. The compounds were extracted from wastewater samples by solid-phase extraction (SPE) and analyzed by High-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS). The results showed that acetaminophen, atenolol and lincomycin were the main individual pollutants usually found in concentrations over 10 μg/L in the sewage influent. In the WWTPs, the concentrations of analgesic acetaminophen, stimulant caffeine, hormones estriol and estradiol decreased by over 99%. On the contrary, the antibiotic sulfamethazine, the antihypertensive metoprolol, and the antiepileptic carbamazepine exhibited removal efficiencies below 30%. Particularly, removal of antibiotics was observed to vary between − 11.2 and 69%. In the primary treatment (physico-chemical processes), the removal of pharmaceuticals was insignificant (up to 28%) and removal of majority of the pharmaceuticals occurred during the secondary treatment (biological processes). The compounds lincomycin, carbamazepine, atenolol, metoprolol, and triclosan showed better removal in WWTPs employing modified activated sludge process with co-existence of anoxic-oxic condition. Further investigation into the design and operational aspects of the biological processes is warranted for the efficient removal of PPCPs, particularly antibiotics, to secure healthy water resource in the receiving downstream, thereby ensuring a sustainable water cycle management.