Construction and Operation of a Submerged Aerated Filter Sewage-Treatment Works

The capacity of the sewage-treatment works at Silchester in Hampshire has been enhanced and the effluent quality improved to a high standard by the installation of a new submerged biological aerated filter plant. Ten prefabricated steel submerged aerated filters reduce BOD and fully nitrify settled domestic sewage from a population equivalent of 20 000.
Comprehensive operating data are presented to demonstrate the ability of single-stage submerged downflow aerated biological filters to produce a nitrified effluent. The final effluent quality remains consistently within consent limits at 4.8 mg/l BOD, 7.0 mg/l SS and 0.5 mg/l NH₃-N, all 95 percentiles. (Consent 7 mg/l BOD, 25 mg/l SS, and 5 mg/l NH₃-N, 95 percentiles.)
Data are presented on total coliform and E. Coli concentrations through the filter plant, showing better than 3 log reductions in the effluent.     

Factors Affecting the Performance of a Packaged Sewage-Treatment Plant

This paper describes the performance of a small packaged plant serving about 70 people and incorporating submerged aerated filters. The diurnal variation was typical of a small sewage-treatment works, and the final effluent was well stabilised with average BOD and amm.-N concentrations of 12 mg/l and 3.8 mg/l respectively.     

Upgrading Biological Filter Effluents Using the TF/SC Process

The trickling filter/solids contact process has been shown to be an excellent means of upgrading biological filter plants in North America, and about 100 plants have been built since 1979 in both cold and warm climates, and on both large and small works. A variety of effluent requirements has been satisfied consistently, including monthly average BOD and SS concentrations of 10 mg/l and 10 mg/l respectively. Key design features are described, including the use of an aerated solids contact tank to flocculate dispersed solids. Also, a flocculator-clarifier with special design features allows the use of high overflow rates and smaller sedimentation tanks.     

Pilot Scale Aerobic Sequencing Batch Reactor for Pig Waste Treatment

A n existing aetated lagoon treating piggery waste was converted into an aerobic sequencing batch reactor (SBR). After the commissioning period, the SBR plant treated piggery wastewater containing BOD and suspended solids (SS) concentrations of 2881 mg/l and 1419 mg/1 respectively, producing an effluent having an average BOD and SS of 18.7 mg/1 and 12.3 mg/1 respectively. The volumetric loadings on the SBR and the process were similar. However, the SBR process operated at a lower mixed liquor suspended solids (MLSS) concentration and shorter sludge retention period. Although the capital and operating costs of the SBR are higher than for the aerated lagoon, the simplicity of operation, the high BOD and SS removal efficiency, and the small land requirement make this type of process an attractive treatment option, particularly in places where land supply is limited and expensive.     

The Production of High-Quality Effluents in Sewage Treatment Using the Biocarbone Process

The Biocarbone process is a new system for water and effluent purification in which biological treatment and physical filtration take place in the same reactor. Because the use of the process for tertiary treatment of sewage effluent had not been fully investigated, a pilot-scale evaluation was undertaken at Severn Trent's Wigston sewage-treatment works. This paper presents the results.
The study corroborates performance information published by the manufacturer. It shows that the process is an alternative to conventional technology for producing fully-nitrified tertiary effluents having low biochemical oxygen demand (BOD) and suspended solids (SS) concentrations.     

Pilot-Plant Study of a New Wastewater Treatment System

Because of severe space limitations for the reconstruction of its sewage-treatment system, the city of Nagoya has evaluated a space-saving wastewater treatment system comprising a solid-liquid separator (SLS) and biological aerated filter (BAF). The SLS is filled with plastic media forming a 2 m thick layer, and influent suspended solids are removed through the media packed zone. The BAF plant has a 2 m thick layer packed with porous ceramic media and air is diffused from the bottom of the tank.
The paper outlines the new treatment system and the ongoing study of the demonstration plant since 1992. It discusses the respective SS and BOD removal rates and concludes by showing that the new system can reduce retention period and plant area compared with the conventional activated-sludge process.     

Disinfection With Peracetic Acid for Domestic Sewage Re-Use in Agriculture

This paper describes a four-month pilot study on peracetic acid disinfection of unchlorinated tertiary effluent for unrestricted re-use in agriculture carried out at West Bari (Italy) sewage-treatment works. Dosages and contact times ranging from 1 to 500 mg/1 and 5 to 60 mins, respectively, indicated that 10 mg/1 of peracetic acid, with a 30-min contact time, achieved the WHO faecal coliform guideline (1000 CFU/100ml). Much higher doses (£400 mg/l and 30 mins) were required to meet the corresponding Californian limit of two colony-forming units/100 ml, which has also been adopted in Italy. Efficient mixing of the disinfectant (in one shot addition) was mandatory - particularly at lower dosages (1–10 mg/l) where there was a higher concentration of suspended solids (>5 mg/l).     

The effects of media size on the performance of biological aerated filters

Biological aerated filters (BAFs) are an attractive process option, particularly when low land usage is required. They can combine BOD, solids and ammoniacal nitrogen removal and can be utilised at both secondary and tertiary stages of wastewater treatment. Media selection is critical in the design and operation of BAFs to achieve effluent quality requirements. Two size ranges, 1.5-3.5 and 2.5-4.5 mm, of a foamed clay called StarLight C were used in pilot-scale reactors. Both performed well as BAF media, with reactor loads up to 12 kg COD m(-3) d and 4 kg suspended solids m(-3) d (based on working volumes). The most consistent effluent was obtained using the smaller medium since, at flow rates above 0.41 min(-1), the BAF using the larger medium produced an effluent containing more than 20 mg l(-1) of suspended solids for over 30 min after backwashing. Up to 70% longer run times, as determined by reaching a set head loss, were recorded for the BAF containing the larger rather than the smaller medium. Additionally, the development of pressure above the smaller medium filter bed tended to be logarithmic rather than linear. Reactor profiles indicated that suspended solids removal did not occur over the full 2.3 m depth of the columns. The BAF containing the smaller medium utilised a mean depth of 1.7 +/- 0.3 m, whereas a mean depth of 2.1 +/- 0.3 m was used by the larger medium BAF. Both the head loss development data and the suspended solids removal profiles indicated that the smaller medium BAF was underperforming as a filter.     

Wind-aerated lagoons for sustainable treatment of wastewaters from small communities

Biological treatment processes that utilise wind‐aerated lagoons have proved popular for small communities because of their negligible sludge production. Scottish Water has recently constructed one such system, known as the Aero‐Fac (North Dakota, USA), and this paper reports on an intensive 12‐month study designed to both monitor the lagoon performance and establish the key design parameters. Over the monitoring period the final effluent complied with both Scottish Environmental Protection Agency discharge consents and Scottish Water performance guarantees for biochemical oxygen demand and total suspended solids, which averaged 9 and 28 mg/L, respectively. The lagoons showed an accelerated growth of algae during the summer months, but this did not adversely affect the final effluent suspended solids. The lagoons also achieved a faecal coliform removal of around 3.4 log and an average effluent ammonia of 7.6 mg/L. However, the ammonia removal was seasonal with a better performance in the summer months, which probably reflects take‐up by the growing algal population over this period. No sludge was wasted from the lagoon over the monitoring period yet it accumulated only sparingly in the lagoons, mainly around the inlet of the primary lagoon. The estimated per capita sludge accumulation rate was 0.0047 m³/person/year. The total capital costs of the scheme were £1.65 million, and of this the lagoon cost was £840 000. The capital costs of £420 per capita make this more expensive than other, similar options, but plant operating costs are significantly reduced.     

Comparison of RBC and SBR Systems for the Treatment of Sewage from Small Communities

This paper describes a study which was carried out to evaluate the performance of two types of small sewage-treatment plant which are commonly available in the UK, i.e. a rotating biological contactor and a sequencing batch reactor. Both systems produced an effluent quality of less than 20 mg/l BOD and 30 mg/l SS; however, the sequencing batch reactor was more consistent in producing a better effluent (i.e. BOD<10 mg/l and SS<20 mg/l) than the rotating biological contactor. The sequencing batch reactor also demonstrated a greater tendency to remove nutrients, although the special design features which were used in this study were believed to have enhanced the rate of nutrient removal     

采用氧化沟工艺的某污水处理厂的设计与运行

某城市污水处理厂采用氧化沟处理工艺,占地省、运行费用低、处理效果好、工作可靠,系统对悬浮物、COD、BOD5的去除率分别为90.5%、73.1%、90.2%,均达到了设计要求.出水各项指标均达到了<污水综合排放标准>(GB 8978-1996)的二级标准.     

The risks from airborne asbestos in the urban environment

The objective of this full‐scale study is to determine the treatment performance of the activated sludge process for treating low strength municipal wastewater. The plant is located in Painesville, Ohio, and discharges its treated effluent into Grand River. The average plant wastewater flow was 3.43 MGD (million gallons per day). The plant performance was evaluated for a 12‐month period in 1989. The low strength municipal wastewater contained 104 mg/L TSS (total suspended solids), 105 mg/L BOD (biochemical oxygen demand), 17.76 mg/L TKN (total kjeldahl nitrogen), 9.66 mg/L NH₃‐N, and 3.90 mg/L P (phosphorus). The treatment performance after various degrees of treatment is as follows: primary treatment: 30% BOD and 54% TSS removal, secondary treatment: 97% BOD and 87% TSS removal, and tertiary treatment: 98% BOD and 98% TSS removal. The primary effluent contained 73 mg/L BOD and 48 mg/L TSS; the secondary effluent contained 3 mg/L BOD and 13 mg/L TSS; and the final effluent contained 2 mg/L BOD and 2 mg/L TSS. The effluent contained 0.22 mg/L NH₃‐N and 0.49 mg/L P, which were far below the US EPA standard of 10 mg/L BOD, 10 mg/L TSS, 1 mg/L NH₃‐N, and 1 mg/L P.     

VALIDATION OF BNR (BIOLOGICAL NUTRIENT REMOVAL) PLANT

Llangefni WwTW receives discharge from the rural town of Llangefni and the local industrial estate and to date this is the first and only BNR plant in Wales. The consents from March 2003 included a reduction in ammonia (NH₄_N) to 1.5 mg/l, suspended solids to 20 mg/l (SS) and Biological Oxygen Demand (BOD) to 7 mg/l and included a new Phosphate (PO₄_P) standard of 2 mg/l. The process selected to meet the new consents was Biological Nutrient Removal (BNR) and was unusual as it was for a small, rural wastewater treatment plant that receives about 26% of its flow from an industrial estate.
During commissioning, the plant produced an average phosphate concentration of 1.0 mg/l and an ammonia concentration of 0.7 mg/l. It was confirmed that to achieve consistent phosphate removal a BOD:P ratio greater than 20:1 is required along with a high VFA (Volatile Fatty Acids) concentration of 200–300 mg/l.     

Full-scale trials of recycled glass as tertiary filter medium for wastewater treatment

Pilot-scale trials at a domestic wastewater treatment works compared the performance of three grades of recycled glass (coarse, medium and fine) when used as tertiary filter media for total suspended solids removal (TSS). Fine glass produced the best effluent quality but blinded rapidly and coarse glass could process three times the flow but with a reduction in final effluent quality. The medium glass offered a compromise with similar flow characteristics to the coarse glass, yet still achieve good solids removal, albeit less than the fine glass. Full-scale studies compared the performance of medium glass with the sand medium that is typically used in this application. There was little difference between them in terms of TSS removal, and they both removed around 75% of TSS from the influent, provided that the solids concentration did not exceed 70mg/l. However, the glass media had superior flow characteristics and was able to treat an additional 8-10% of the influent following the backwash cycle. Over the study period, the influent to the filters had an average TSS concentration of 38mg/l and produced an effluent with an average of 15mg TSS/l. In order to design for an average TSS concentration of 20mg/l, the maximum solids loading on the medium should not exceed 0.25kg solids/m(3)/h. Selecting recycled glass as a tertiary filter medium will give a 10% reduction in the amount of media required, compared to sand. It also carries with it the benefits of using a recycled material, and although these are more difficult to quantify they include: reduced CO(2) emissions and use of a more sustainable product that promotes favourable publicity and positive environmental reporting.     

Influence of operational conditions on the performance of a mesh filter activated sludge process

Recently, a new type of wastewater treatment system became the focus of scientific research, the mesh filter activated sludge system. It is a modification of the membrane bioreactor where a membrane filtration process serves to separate the sludge from the purified effluent. The difference is that a mesh filter is used instead of the membrane. Due to the much larger pore size of the mesh, the effluent is not of the same excellent quality as with membrane bioreactors. Nevertheless, it still resembles the quality of the now most widely used standard treatment system, where settling tanks are used to retain the activated sludge. At the same time, the new system features all the other advantages of membrane bioreactors including elevated sludge concentrations resulting in decreased volumina of basins and complete substitution of the settling tank. Therefore, this process presents a potential future alternative where a small footprint of the plant is required. However, so far only a few preliminary studies on this innovative process type have been done. In this paper, the effects of suspended solids concentration, flux rate as well as aeration rate on the effluent quality are discussed. Furthermore, the characteristic of the sludge floc was identified as a factor of vital importance. Therefore, another influencing parameter, the food to microorganism (F/M) ratio, which is known to have a significant effect on floc characteristics, was studied. The main result demonstrated that the process was very effective under most of the operation conditions. The suspended solids concentration in the effluent was below 12 mg l(-1), the average COD in the effluent was between 24 and 45 mg l(-1) and the BOD(5) was lower than 5 mg l(-1). High flux rates of up to 150 l m(-2)h(-1) were also achieved.     

The use of stochastic models in the interpretation of historical data from sewage treatment plants

A 3-yr historical record of sewage treatment plant performance has been evaluated graphically and with time series methodology. Models relating influent biochemical oxygen demand to effluent biochemical oxygen demand, mixed liquor suspended solids, temperature, and hydraulic detention time were constructed. Four possible definitions of plant efficiency were defined and studied as well. The use of efficiency rather than effluent BOD for modeling performance was not helpful. A logarithmic transformation of BOD seems to be a better metric than BOD itself. Studying historical records should lead to an improved understanding of plant dynamics. Time series methods seem to be one useful tool for this work.     

Milestones in the Development of the Activated-Sludge Process Over the Past Eighty Years (Abridged)

The biological filter was introduced during the latter part of the last century but, in 1913, a radical new process was developed which resulted in a four-fold reduction in the size of sewage-treatment plants. This new method was called the 'activated-sludge process', and whilst biological filters are still in use - especially for small works - activated sludge is now the dominant secondary treatment process and is the 'engine'around which modern treatment systems are constructed.
This paper (a) reviews the milestones in the evolution of the activated-sludge process from 1913 to 1954, centering on reliable removal of BOD and suspended solids, (b) highlights the improvements in design capabilities (1955-74), with the emphasis on the attainment of consistent nitrification, and (c) discusses the removal of nitrogen and phosphorus (1975-97), with brief reference to computer modelling and the control of sludge properties.     

Leachate Collection, Treatment and Disposal

As landfills become larger, the enormous quantities of putrescible wastes which they contain have increased the potential to generate highly polluting leachates as they decompose anaerobically over many years. If severe environmental impacts are to be avoided, operators must control these liquors: many landfill proposals stand or fall on the ability of the operator to demonstrate that leachate can be collected, managed and disposed of in an environmentally acceptable manner. During the early years of tipping in containment cells, high BOD and COD values (to 50 000 mg/l or more) are measured, with very high ammonia concentrations (to more than 1000 mg/l as N) persisting for many years.
The authors have been involved with the full-scale on-site treatment of leachates to high standards in automated aerated lagoon plants since the early 1980s. The first plant was constructed in 1982, and a further seven have since been built at landfills throughout the UK, with many more at various stages of design and construction – both in the UK and overseas.
This paper describes detailed operational experiences from several of these landfill sites, with particular emphasis on the reduction of ammonia concentrations to low values. The use of reed-bed treatment schemes as effluent polishing facilities is also discussed.     

MEMBRANE BIOREACTORS AND CONSTRUCTED WETLANDS FOR TREATMENT OF RENDERING PLANT WASTEWATER

The performance of a novel industrial membrane bioreactor (MBR) comprising denitrification, nitrification and ultrafiltration for the secondary treatment of primary treated animal rendering wastewater has been compared with an experimental, low-cost and novel vertical-flow constructed wetland planted with Typha latifolia L. (Reedmace or Broad-leaved Cattail). The process wastewater followed pre-treatment by dissolved air flotation (DAF). The mean DAF effluent gave highly variable chemical oxygen demand (COD) and ammonia concentrations of 5816 (standard deviation (SD): 3005.0) and 614 (SD: 268.7) mg/l, respectively. The mean MBR effluent for COD and ammonia was 37 and 86 mg/l, respectively. The mean treatment performance of the constructed wetland for COD, ammonia and suspended solids was 205, 67 and 57 mg/l, respectively.