Nutrient loading on subsoils from on-site wastewater effluent, comparing septic tank and secondary treatment systems

The performance of six separate percolation areas was intensively monitored to ascertain the attenuation effects of unsaturated subsoils with respect to on-site wastewater effluent: three sites receiving septic tank effluent, the other three sites receiving secondary treated effluent. The development of a biomat across the percolation areas receiving secondary treated effluent was restricted on these sites compared to those sites receiving septic tank effluent and this created significant differences in terms of the potential nitrogen loading to groundwater. The average nitrogen loading per capita at 1.0 m depth of unsaturated subsoil equated to 3.9 g total-N/d for the sites receiving secondary treated effluent, compared to 2.1 g total-N/d for the sites receiving septic tank effluent. Relatively high nitrogen loading was, however, found on the septic tank sites discharging effluent into highly permeable subsoil that counteracted any significant denitrification. Phosphorus removal was generally very good on all of the sites although a clear relationship to the soil mineralogy was determined.     

Mass balance and isotope effects during nitrogen transport through septic tank systems with packed-bed (sand) filters

Septic tank systems are an important source of NO3(-) to many aquifers, yet characterization of N mass balance and isotope systematics following septic tank effluent discharge into unsaturated sediments has received limited attention. In this study, samples of septic tank effluent before and after transport through single-pass packed-bed filters (sand filters) were evaluated to elucidate mass balance and isotope effects associated with septic tank effluent discharge to unsaturated sediments. Chemical and isotopic data from five newly installed pairs and ten established pairs of septic tanks and packed-bed filters serving single homes in Oregon indicate that aqueous solute concentrations are affected by variations in recharge (precipitation, evapotranspiration), NH4+ sorption (primarily in immature systems), nitrification, and gaseous N loss via NH3 volatilization and(or) N2 or N2O release during nitrification/denitrification. Substantial NH4+ sorption capacity was also observed in laboratory columns with synthetic effluent. Septic tank effluent delta15N-NH4+ values were almost constant and averaged +4.9 per thousand+/-0.4 per thousand (1 sigma). In contrast, delta15N values of NO3(-) leaving mature packed-bed filters were variable (+0.8 to +14.4 per thousand) and averaged +7.2 per thousand+/-2.6 per thousand. Net N loss in the two networks of packed-bed filters was indicated by average 10-30% decreases in Cl(-)-normalized N concentrations and 2-3 per thousand increases in delta15N, consistent with fractionation accompanying gaseous N losses and corroborating established links between septic tank effluent and NO3(-) in a local, shallow aquifer. Values of delta18O-NO3(-) leaving mature packed-bed filters ranged from -10.2 to -2.3 per thousand (mean -6.4 per thousand+/-1.8 per thousand), and were intermediate between a 2/3 H2O-O+1/3 O2-O conceptualization and a 100% H2O-O conceptualization of delta18O-NO3(-) generation during nitrification.     

复合式竹丝填料生物反应器处理化粪池出水

为寻找适合化粪池出水的处理工艺,采用批式试验研究了复合式竹丝填料生物反应器对化粪池出水中COD、SS的去除效果。结果表明:复合式竹丝填料生物反应器能有效去除化粪池出水中的COD和SS,平均去除率分别达到了85.4%和90%以上;复合式竹丝填料生物反应器的微生物数量较多、微生物链较长、微生物种群丰富;复合式竹丝填料生物反应器中的污泥增加量极少。将复合式竹丝填料生物反应器内的活性污泥和竹丝分开组成两个独立的生物反应器并处理化粪池污水,结果发现,竹丝生物膜反应器能在短期(18h)内超过活性污泥反应器的处理效果,且竹丝生物膜反应器的产泥量很低。可见,竹丝填料较为适合处理化粪池出水,是一种价格低廉、污染少、运行管理费用较低的良好填料。     

Phosphorus concentrations in the River Dun, the Kennet and Avon Canal and the River Kennet, southern England

Variations in phosphorus (P) concentrations in an agriculturally impacted river draining a Chalk aquifer and an associated canal in the west of the Thames Basin, southern England are examined and linked to agricultural and sewage sources and within river/canal process controls. The study area comprises the River Dun, the adjacent River Kennet and the Kennet and Avon (K&A) Canal. Large seasonal variations are observed for soluble reactive phosphorus (SRP) and dissolved silicon (Si) with low concentrations in the spring and summer times when biological activity is high. The K&A Canal shows the largest SRP and Si concentration declines. This reflects high biological activity coupled with higher temperatures and higher water residence times. The extent of SRP removal is examined in relation to organic (uptake/release with phytoplankton growth/decay) and, to a lesser extent, inorganic (SRP coprecipitation with calcite) mechanisms. Boron (B) is used as a tracer of sewage sources. Agricultural inputs of both dissolved and particulate P (PP) can be important particularly under conditions where the catchment is wet and near surface/overland flow is important: sewage treatment works effluent and septic tank discharges to groundwater also probably provide a major component of the SRP occurring within the water column. The canal, and to a lesser extent the river, acts as sink for P in sewage effluent sources due to the high biological activity especially during the spring and summer. The aquifer probably acts as a major sink for agricultural and septic tank inputs of P.     

Virus removal within a soil infiltration zone as affected by effluent composition, application rate, and soil type

The column studies presented in this paper simulated the infiltrative surface of onsite wastewater systems where effluent is applied and where a biomat may form. Two bacteriophages, MS-2 and PRD-1, were used as surrogates for human pathogenic enteric viruses during two tracer tests. A vacuum manifold was used to simulate the drainage effects of an underlying unsaturated soil profile, allowing for the collection of percolate samples at 4 cm immediately below the infiltrative surface. The impact of effluent applied (septic tank effluent (STE) or a simulated ground water), soil type (medium sand or sandy loam), hydraulic loading rate (5 or 25 cm/day) and method of application (four equivalent daily doses or 24 equivalent micro-doses per day) on the removal of viruses were investigated. These unsaturated mini column experiments demonstrated that the removal of viruses within an infiltrative surface zone (of approximately 4 cm) generally improved over time under the conditions studied. An exception occurred in sand-filled columns dosed with STE where the removal of PRD-1 decreased after a period of effluent application. Statistical analysis conducted on the calculated percent removal demonstrated that the quality of the effluent applied to the infiltrative surface is important for removal of MS-2 and PRD-1. Hydraulic loading rate also proved important in the removal of viruses. At the time of tracer test 2, columns dosed at the higher HLR (25 cm/day) had higher percent removals for both MS-2 and PRD-1. Soil type altered the removal of PRD-1 at the time of the second tracer test, at which time sandy loam had higher removal rates for PRD-1. No significant differences were observed between columns dosed four times daily and those dosed 24 times daily for either bacteriophage at either of the tracer test time points. These data suggest that over a relatively short period of operation the infiltrative surface of soil based wastewater treatment systems can achieve much higher removal then initially measured shortly after startup.     

高效初沉发酵池处理城市污水的中试研究

应用生物絮凝沉淀和水解发酵耦合工艺,将传统的初沉池改造为集进水悬浮固体的沉淀分离和沉淀污泥的产酸发酵为一体的高效初沉发酵池,以优化碳源结构,提高后续工艺的污泥活性和脱氮除磷能力。在水力停留时间为0.75 h、悬浮污泥絮体层界面高度不低于高效初沉发酵池有效池深的70%、SRT为4 d的条件下,考察了高效初沉发酵池对进水水质的改善效果。结果表明:高效初沉发酵池对SS的去除率为78%,是普通初沉池的近2倍;出水VSS/SS均值为71.9%,较普通初沉池提高了17.3%;出水C/N和C/P值较进水值分别提高了33%和14%,且明显高于污水厂普通初沉池出水水质。碳源结构的改善提高了后续生物处理工艺的脱氮除磷效果,对TP的去除率稳定在90%～98%。     

Hydraulic and purification behaviors and their interactions during wastewater treatment in soil infiltration systems

Four three-dimensional lysimeters were established in a pilot laboratory with the same medium sand and either an aggregate-laden (AL) or aggregate-free (AF) infiltration surface and a 60- or 90-cm soil vadose zone depth to ground water. During 48 weeks of operation, each lysimeter was dosed 4 times daily with septic tank effluent (STE) at 5 cm/d (AL) or 8.4 cm/d (AF). Weekly monitoring was done to characterize the STE, percolate flow and composition, and water content distributions within the lysimeters. Bromide tracer tests were completed at weeks 0, 8, and 45 and during the latter two times, ice nucleating active (INA) bacteria and MS-2 and PRD-1 bacteriophages were used as bacterial and viral surrogates. After 48 weeks, soil cores were collected and analyzed for chemical and microbial properties. The observations made during this study revealed a dynamic, interactive behavior for hydraulic and purification processes that were similar for all four lysimeters. Media utilization and bromide retention times increased during the first two months of operation with the median bromide breakthrough exceeding one day at start-up and increasing to two days or more. Purification processes were gradually established over four months or longer, after which there were high removal efficiencies (>90%) for organic constituents, microorganisms, and virus, but only limited removal of nutrients. Soil core analyses revealed high biogeochemical activity within the infiltrative zone from 0 to 15 cm depth. All four lysimeters exhibited comparable behavior and there were no significant differences in performance attributable to infiltrative surface character or soil depth. It is speculated that the comparable performance is due to a similar and sufficient degree of soil clogging genesis coupled with bioprocesses that effectively purified the wastewater effluent given the adequate retention times and high volumetric utilization's of the sand media.     

Contamination of the Chalk Aquifer by Chlorinated Solvents: A Case Study of the Luton and Dunstable Area

A detailed investigation of contamination by chlorinated solvents of the Chalk Aquifer underlying the towns of Luton and Dunstable was undertaken to assess the extent, causes and mechanisms of pollution. The research programme incorporated land-use surveys, regional groundwater surveys, monitoring of groundwater abstraction points and aquifer profiling by means of the drilling of observation boreholes, the analysis of the recovered core material and the depth sampling of these and other boreholes.
Low-level solvent contamination of the Chalk Aquifer was found to be widespread with 'hotspots'of higher concentrations. At the drilling sites, both the saturated and unsaturated zones were contaminated with solvents, although free product was not observed. The presence of an additional contaminant, oil, at some sites was noted to influence the distribution of solvents within the aquifer.
Clean-up of the aquifer is not a practical option, and treatment of the groundwater at the abstraction points has been adopted.     

武汉火神山、雷神山医院污水处理工程设计

火神山、雷神山医院是为集中收治新型冠状病毒肺炎(COVID-19)患者而设立的传染病专科医院,其污水处理系统设计均采用"预消毒接触池+化粪池+提升泵站(含粉碎格栅)+调节池+MBBR生化池+混凝沉淀池+接触消毒池"处理工艺。MBBR工艺实现了低温下污水中污染物的高效去除,两级消毒工艺保障了病毒100%消灭,同时污水站地基下方按垃圾填埋场标准铺设HDPE膜,保障雨水污水全收集并进行消毒后排放,污泥经消毒脱水后按危险废物集中清运处理,废气统一收集经除臭消毒后排放,实现雨污水、污泥、废气的全收集和全处理。当前,火神山、雷神山医院污水处理系统运行稳定,相关出水指标均已达到设计要求,其中COD稳定低于50mg/L,氨氮稳定在2 mg/L以下,余氯稳定在13 mg/L附近,污染物去除与消毒效果均十分稳定。     

Intermittent filtration of wastewater--removal of fecal coliforms and fecal streptococci

Removal of fecal coliforms and fecal streptococci was monitored over a period of 13 months in 14 buried pilot scale filters, treating septic tank effluent. The effects of grain size, hydraulic dosing rate and distribution method were investigated. Two different natural sands (sorted sand and unsorted sand) and three different types of light weight aggregates (LWA 0-4 mm, LWA 2-4 mm and crushed LWA 0-3 mm) were used. Intermittent dosing rates from 20 to 80 mm/day in 12 doses per day were applied to the filters by uniform pressure distribution or point application by gravity dosing. Removal of fecal coliforms was more than three orders of magnitude higher in the media with the finest grain sizes (unsorted sand) as compared to the coarsest media (LWA 0-4 mm and LWA 2-4 mm) operated under same conditions. Fecal streptococci were determined only in effluent from filters with LWA 0-4 mm and LWA 2-4 mm. Higher removal of fecal coliforms was observed in pressure dosed filters compared to gravity dosed filters. A lower removal was observed by increasing the hydraulic dosing rate. Minimum retention time was found to be a key parameter for predicting removal of bacteria in unsaturated, aerobic filters. At minimum retention times lower than about 50 h, there was a correlation of 0.96 between retention time and removal of fecal coliforms. Retention times longer than 50 h gave almost complete removal of fecal coliforms.     

Mathematical model for predicting sludge accumulation in septic tanks based on operational parameters: effect of hydraulic mixing

Reporting sludge accumulation in septic tanks as a constant rate is no longer accepted, and there is a need for a model that predicts sludge accumulation in septic tanks taking into consideration the continuous consumption of sewage solids by microorganisms. This study presents the development of mathematical model that predicts sludge accumulation in septic tanks and to investigate the effect of mixing on solids digestion. The mathematical model takes into consideration the effect of different operational parameters (influent and effluent) as well as the bacterial kinetics in predicting the sludge accumulation in septic tanks. The model predicts with R² > 0.88 the sludge accumulation rate in standard septic tank calculated by empirical models developed by Weibel in 1955, and by Bounds in 1995. The model was also used to estimate the typical pump‐out interval for different tank volumes and the sludge accumulation inside septic tanks at different operational parameters.     

斜管沉淀池-活性砂过滤工艺在城镇污水处理厂中的应用

针对株洲南部区域污水进水水质浓度较低、容易出现短时高浓度的情况,采用斜管沉淀池-活性砂滤池对二沉池出水进行深度处理,以保证其出水水质达到GB 189182002《城镇污水处理厂污染物排放标准》一级A标准。经过深度处理后,COD、SS、BOD5、NH3-N、TP去除率均优于一级A标准,出水可作为再生水使用。对此工艺进行技术经济分析,结果表明该工艺具有占地面积小、高效节能等优点,可为同类污水处理技术提供参考。     

The impact of co-contaminants and septic system effluent quality on the transport of estrogens and nonylphenols through soil

The impact that varying qualities of wastewater may have on the movement of steroid estrogens through soils into groundwater is little understood. In this study, the steroid estrogens 17β-estradiol (E2) and estrone (E1) were followed through batch and column studies to examine the impact that organic wastewater constituents from on-site wastewater treatment systems (i.e., septic systems or decentralized systems) may have on influencing the rate of transport of estrogens through soils. Total organic carbon (TOC) content (as a surrogate indicator of overall wastewater quality) and the presence of nonyl-phenol polyethoxylate surfactants (NPEO) at concentrations well below the critical micelle concentration were independently shown to be indicative of earlier breakthrough and less partitioning to soil in batch and column experiments. Both NPEO and wastewater with increasing TOC concentrations led to shifts in the equilibrium of E1 and E2 towards the aqueous phase and caused the analytes to have an earlier breakthrough than in control experiments. The presence of nonylphenols, on the other hand, did not appreciably impact partitioning of E1 or E2. Biodegradation of the steroids in soil was also lower in the presence of septic tank effluents than in an organic-free control water. Furthermore, the data indicate that the rate of movement of E1 and E2 present in septic tank effluent through soils and into groundwater can be decreased by removing the NPEOs and TOC through wastewater treatment prior to sub-surface disposal. This study offers some insights into mechanisms which impact degradation, transformation, and retardation, and shows that TOC and NPEO surfactants play a role in estrogen transport.     

Power economy characteristics of an activated sludge aeration tank

The air feed rate to meet a given oxygen uptake rate in the activated sludge aeration tank was expressed by using the concept of the air diffuser performance, previously proposed by the present authors. Using the relationship between the BOD removal and the oxygen uptake rate, a procedure to predict the power economy, which is defined as the amount of BOD removed per unit power consumption of the air feeding, and the effluent quality of the activated sludge process under various operating conditions was presented. The effect of operating parameters in the tank; the MLSS concentration; the hydraulic retention time and the BOD loading on the power economy and the effluent quality were extensively evaluated. The results calculated by the proposed procedure were compared with the statistic data of operating conditions in the municipal wastewater treatment plants in Japan. A method to improve the effluent quality while maintaining a high power economy was also discussed.     

Acute toxicity of unbleached kraft mill effluent (UKME) to the opossum shrimp, Neomysis americana smith

Ninety-six hour TL₅₀ values of unbleached kraft mill effluent (UKME) for Neomysis americana were found to range from concentrations of 3.29–6.85 per cent at 26–28°C and 3.90–7.30 per cent at 16–18°C. Differences between batches of effluent proved insignificant in experiments at each temperature regime. Furthermore, UKME did not lose its toxicity when stored for 5–7 days at 4°C. A concentration of 20 per cent effluent killed 100 per cent of the organisms in 8 of the 12 bioassays. Slope functions and confidence limits of TL₅₀ were calculated. Toxicity did not appear to be correlated with the Biochemical Oxygen Demand (BOD) of individual batches of raw effluent.     

污水处理厂SBR池提标改造工艺设计

某污水厂将设计出水水质由二级标准提高至一级B排放标准,为此对SBR池进行了改造。在不增加构筑物占地面积、不改变运行工况的基础上,将SBR池中的每一格重新划分为厌氧池、缺氧池、好氧池和强化好氧池等4个部分,通过试验确定了设计参数。实际运行表明,改造工艺强化了SBR池的除污能力,从而使该厂的出水水质达到了一级B排放标准。     

A septic tank‐UASB combined system for domestic wastewater treatment: a pilot test

A 250 L and a 550 L pilot scale Up‐Flow Anaerobic Sludge Blanket (UASB) reactors having different reactor height were fed septic tank effluents and operated at ambient temperatures of 0°C to 30°C. Both UASB reactors were fed intermittently at least 8 times per Hydraulic Retention Time (HRT) and the performance was monitored at 4d and 1d HRT. The removal efficiencies of Total Suspended Solid (TSS) and Total Chemical Oxygen Demand (COD_t) were about 59–68% and 54–59%, respectively, for both reactors at both HRT. The TSS and CODt removal efficiencies of Septic tank – UASB combined system were above 80% for both HRTs tested. The average biogas yields were almost same at 4d and 1d HRT, representing 31(±3)% of influent CODt. The nitrogen and phosphorous removal efficiency was an average 20–30%. The tested system can become a suitable low cost yet effective option.     

Environmental aspects of the use of NTA as a detergent builder

The behaviour, fate and significance of the detergent builder nitrilotriacetic acid (NTA) has been reviewed with particular reference to the removal of NTA during wastewater treatment and the effects of NTA on heavy metal solubility both during treatment and in the receiving environment. It is concluded that NTA removal during secondary biological treatment is subject to considerable variation, both temporal and between works as a result of changes in NTA load, temperature, water hardness and treatment process parameters. As a result of such variability, effluent NTA concentrations may be sufficient to mobilise heavy metals resulting in metal contamination of receiving waters and potable waters, particularly in areas of low effluent dilution and high water re-use. Removal of NTA during primary sedimentation and septic tank treatment is concluded to be predominantly due to adsorption to the sludge solids while removal in anaerobic sludge digestion is subject to operational characteristics of the treatment works. Disposal of NTA contaminated sludge to land may contaminate groundwaters and affect heavy metal speciation, while the disposal of contaminated sludge or sewage to sea may result in toxic algal blooms, in addition to effects on metal speciation.     

液氯应用于地表水厂应急除锰研究

针对水厂原水夏季锰超标带来的出厂水浊度、色度超过滤后水的问题,经对比试验和分析论证采用液氯氧化除锰方案.通过在预氧化接触池投加氯,出厂水中锰从原水的0.1-2.0mg/L降低到0.05 mg/L以下,色度从原水的50-80度降低至5度,工艺简单,易于操作.同时调查分析了水厂锰的来源及变化,并针对水厂设计以及液氯除锰中需...     

水解酸化池预处理低碳生活污水的效能分析

为了提高低碳氮比生活污水的脱氮效能,在缺氧池前设置水解酸化池,通过水解酸化作用改善进水碳源,同时对回流剩余污泥进行降解,以期达到改善进水碳源可生化性、提高其可利用率、减少外碳源投加量并实现污泥减量的目的。分别考察了水解酸化池对污水单独进行预处理以及对污水和回流污泥同时进行预处理情况下的作用效能及其对系统脱氮的影响。结果表明:两种预处理条件下,理论B/C值都大于0.65,出水SCOD/COD的平均值和出水VFA浓度均高于进水,单独污水水解酸化的出水SCOD减少较多,对TN的去除率仅为47.8%;回流剩余污泥后,温度>20℃且每日分4次共回流20 L剩余污泥的TN去除效果明显优于单独污水水解酸化和温度<20℃且每日分2次共回流10 L的运行效果,两种回流量条件下对TN的去除率分别为71.9%和66.1%,污泥减量率分别为58%和56.3%。