Operating experiences with columnar denitrification

The columnar denitrification process has emerged as a proved and accepted method for removing nitrates from wastewaters. This paper discusses operating experiences while removing nitrogen in effluent polishing filters at an activated sludge plant in Western Pennsylvania. The effect of temperature on removal efficiency and the interrelationship of the denitrification filters to other treatment units is discussed. Operating procedures have been developed to accommodate nitrogen gas buildup in the Denite filters and operating data is included to illustrate simultaneous removal of nitrates and suspended solids. Ample time will be provided to discuss the operation of this type of plant.     

Effects of run‐of‐the‐river hydropower plants on the surface water quality in the Solakli stream watershed,Northeastern Turkey

In recent years, Turkey has turned its attention to alternative energy sources rather than fossil fuels. The Eastern Black Sea Region of Turkey has steep mountains with hilly topography and has large potential in terms of energy production with run‐of‐the‐river hydropower plants (RHPPs). In this study, the effects of two RHPPs on some water quality parameters were examined in the Solakl? stream watershed. This research was conducted over the course of 12 months (January–December 2014). In total, 12 sampling points were selected and various water quality parameters, such as temperature, pH, dissolved oxygen, total suspended solids, electrical conductivity, total dissolved solid, chloride and salinity, were monitered at each point. Statistically, significant changes occured in water quality parameters such as total suspended solids, pH and temperature. In particular, total suspended solids ranged from 10 to 440 mg/L.These results suggest that the RHPP negatively effect water quality and quantity in the main stream in both the operational and constructional phases.     

Slow sand filtration as a technique for the tertiary treatment of municipal sewages

The investigation was designed to demonstrate the viability, or otherwise, of slow sand filtration as a means of tertiary treatment for secondary effluents derived from conventional aerobic, biological treatment processes operating with municipal wastewaters. Secondary effluents derived from both an activated-sludge plant and from a percolating filtration plant were employed.The basic slow sand filtration unit used consisted of a 140 mm i.d. perspex cylinder, 2.65 m in height containing a 950 mm depth of fine sand. Treatment rates were either 3.5 or 7.0 m d⁻¹ and the sand used was of an effective size initially of 0.3 mm and then later of 0.6 mm.This investigation has demonstrated that a laboratory-scale slow sand filtration unit is capable of consistently removing at least 90% of the suspended solids, more than 65% of the remaining BOD and over 95% of the coliform organisms from the settled effluent from an operational percolating filter plant. The length of operational run averaged 20 days at 3.5 m d⁻¹ and 13 days at 7.0 m d⁻¹. Slightly inferior results were achieved when using the settled effluent from an operational activated sludge unit.Further investigation employing a horizontal-flow gravel pre-filter demonstrated that at flows of 2 m h⁻¹ with a contact time of 33 min up to 82% of the suspended solids in the secondary effluent could be removed prior even to slow sand filtration.     

A nitrification model for the contact stabilization activated sludge process

A kinetic model of the contact stabilization process has been developed and experimentally verified with the aid of bench-scale activated sludge units treating domestic sewage. The model provides information on the relationship between the design parameters (process loading, temperature, residence time distribution) and process performance (sludge, production, oxygen uptake, COD-removal, organic nitrogen conversion, nitrification and effluent suspended solids). An oxygen equivalence mass balance equation, which is applicable to all activated sludge process modifications is proposed and may be used in the design and operation of these processes.     

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.     

Effects of sedimentation on removal of faecal coliform bacteria from effluents in estuarine water

Faecal coliform deposition rates with estuary type suspended solids have been examined in laboratory experiments. Faecal coliform deposition rates in estuary water increased proportionately with suspended solids concentration, whereas faecal coliform deposition rates in effluent/seawater mixture showed no correlation with suspended solids concentration.

Deposition of estuary water suspended solids showed correlation with time, whereas deposition of effluent suspended solids showed no correlation with time. The adsorption efficiency experiments suggested immediate adsorption of some of the faecal coliforms onto both types of suspended solids and no difference in adsorption potential.

Therefore, it appears that the contrasting effects on faecal coliform deposition can be attributed to the different deposition potential of each type of suspended solids and not to the adsorption process.     

Blanket dynamics in upflow suspended bed

A one-dimensional model for the spatio-temporal variation of solids fraction in the blanket considering both the hydrodynamic dispersion and the convection effects was proposed in this study. The model equation was a wave equation whose solution presented shock-wave like characteristic. The model output predicted that the distribution of the solids fraction in the blanket would, firstly, evolve to a uniform distribution at a lower solids fraction. Afterward, the blanket would compact itself to another uniform distribution at a higher solids fraction. Experimental works with synthetic raw water coagulated with PACl suspended in a lab-scale suspended bed confirmed the theoretical predictions. The solids flux plot was constructed with underdosed, optimal and overdosed suspensions. Change in coagulant dose would affect the blanket height and the response time. The solids flux curve was shifted accordingly. The "optimal' operational condition for the upflow suspended bed that produced the lowest effluent turbidity was identified and discussed.     

Investigation to replace the conventional sedimentation tank by a microstrainer in the rotating disc system

The function of the microstrainer in removing suspended solids from the effluent of the rotating disc system was studied. Furthermore the SS removal efficiency of the microstrainer was compared with that of the conventional sedimentation tank. It was found that in connection with the complete biological treatment in the rotating disc system, the microstrainer was more efficient in removing suspended solids than the conventional sedimentation tank, and that under the dry-weather-flow condition an effluent SS concentration of 10 mg 1⁻¹ could be obtained with the microstrainer at a surface loading rate of 10–15 m h⁻¹.     

The effect of influent temperature variations in a sedimentation tank for potable water treatment--a computational fluid dynamics study

A computational fluid dynamics (CFD) model is used to assess the effect of influent temperature variation on solids settling in a sedimentation tank for potable water treatment. The model is based on the CFD code Fluent and exploits several specific aspects of the potable water application to derive a computational tool much more efficient than the corresponding tools employed to simulate primary and secondary wastewater settling tanks. The linearity of the particle conservation equations allows separate calculations for each particle size class, leading to the uncoupling of the CFD problem from a particular inlet particle size distribution. The usually unknown and difficult to be measured particle density is determined by matching the theoretical to the easily measured experimental total settling efficiency. The present model is adjusted against data from a real sedimentation tank and then it is used to assess the significance of influent temperature variation. It is found that a temperature difference of only 1 degrees C between influent and tank content is enough to induce a density current. When the influent temperature rises, the tank exhibits a rising buoyant plume that changes the direction of the main circular current. This process keeps the particles in suspension and leads to a higher effluent suspended solids concentration, thus, worse settling. As the warmer water keeps coming in, the temperature differential decreases, the current starts going back to its original position, and, thus, the suspended solids concentration decreases.     

Correlations of performance for activated sludge using multiple regression with autocorrelation

A method is developed to correlate activated sludge response variables, such as SVI, effluent volatile suspended solids or effluent BOD, with state variables such as F/M ratio, influent BOD, dynamic sludge age, etc. The method is based on multiple linear regression with autocorrelated errors. The method was applied to three data sets from two full-scale activated sludge plants; one a regional municipal utility, the other an industrial facility. Highly statistically significant models were found which could explain 65–82% of the variability in effluent total oxygen demand, 22–60% in effluent volatile suspended solids and 48–88% in sludge volume index. It was only necessary to model up to second order lags. The models were tested for bias using different data sets and produced correlation coefficients between predicted and observed values as high as 0.96. These results show that useful predictive relationships can be developed for full-scale activated sludge processes. The methods could be used to develop a range of automatic process control schemes.     

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.     

应用工艺智能优化控制系统降低污水厂能耗

生物工艺智能优化系统（BIOS）是一个前馈优化系统，通过获得A／O工艺实时的在线数据（如氨氮、硝酸盐氮、进水流量、混合液悬浮物浓度），BIOS系统不断进行模拟计算，然后按照生物反应器进水的污染物负荷状况来提供最佳的DO设定值；同时为达到最佳的TN去除率，BIOS系统还对好氧区回流至缺氧区的内回流比（IRQ）进行了优化。BIOS系统在美国康涅狄格州En-field污水厂的实际应用情况表明，该系统能提高脱氮效率36％，同时降低曝气量19％。     

Denitrification of Wastewater: Operating Experiences in the US and Pilot-Plant Studies in the UK

Due to the EC urban wastewater treatment Directive, considerable attention has been focused on nitrogen removal, particularly from biological filter nitrified effluents. The paper presents a reliable and proven full-scale fixed-film denitrification system installed in the US and evaluated on pilot scale by Severn Trent Water. Methanol has been used as a carbon source dosed prior to the deep-bed sand filter. The filter removes considerable suspended solids as well as providing the hydraulic retention and surface area for the growth of the biological denitrifying bacteria. Flow sheets of typical US installations are given and operational data with costs are presented for the pilot-plant evaluation.     

应用膜生物反应器处理生活污水的研究

介绍了膜生物反应器（ｍｅｍｂｒａｎｅｂｉｏｒｅａｃｔｏｒ）应用于处理生活污水的研究。实验结果表明，出水中几乎无悬浮物和浊度，对有机物和含氮化合物的去除效率很高。另研究了膜通量与工作压力、冲击负荷、曝气强度等运行条件之间的关系，并对膜生物反应器的能耗问题进行了较详细的研究。     

Influence of hydraulic shock loads and TDS on the performance of large-scale CETPs treating textile effluents in India

The present study relates to the influence of hydraulic shock loads and total dissolved solids (TDS) on the performance of three large-scale common effluent treatment plants (CETPs) treating textile effluents, which is generated from clusters of small-scale industries in the state of Rajasthan in India. Of the three CETPs, two having capacities 7.0 and 9.0 million liters per day (mld) are located in Pali and one of capacity 6.0 mld in Balotra, District Barmer. Wastewater from about one thousand small-scale industries is treated in these CETPs. The effects of hydraulic shock loads and TDS on effluent data from secondary clarifier for parameters biochemical oxygen demand (BOD) and suspended solids (SS) for CETPs at Pali, and chemical oxygen demand (COD) and SS for the CETP at Balotra were studied. It was observed that the effluent BOD and SS remained within the prescribed limits for CETP Pali at 30% increased flow rate, whereas effluent COD and SS at 30% increased flow rate for CETP Balotra exceeded the prescribed limits and the CETP could sustain 20% increased flow rate. The shock loading analysis revealed that CETP Balotra had reduced capacity to sustain shock loads by 10% as compared to CETP Pali due to the presence of high TDS (15,000-20,000 mg/l). High TDS interfered with the oxygen transfer necessary for biological metabolism, thereby affected the efficiency of activated sludge process. Hence, activated sludge process treating high TDS effluents are more sensitive to hydraulic shock loads and prone to process upsets.     

Incorporation of inorganic material in anoxic/aerobic-activated sludge system mixed liquor

In the bioreactor of the nitrification denitrification (ND)-activated sludge system, the mixed liquor is made up of organic and inorganic materials. In the current design procedures and simulation models, the influent wastewater characteristics and biological processes that influence the bioreactor mixed liquor organic solids (as volatile suspended solids, VSS, or COD) are explicitly included. However, the mixed liquor total suspended solids (TSS, i.e. organic+inorganic solids) are calculated simply from empirical ratios of VSS/TSS. The TSS concentration is fundamental in the design of secondary settling tanks and waste activated sludge disposal. Clearly, the empirical approach to obtaining an estimate for TSS is not satisfactory within the framework of a fundamentally based model. Accordingly, the incorporation of the inorganic material present in the influent wastewater into ND-activated sludge system mixed liquor was investigated. From an experimental investigation into the distribution of inorganics in the influent, mixed liquor and effluent of a laboratory-scale ND-activated sludge system, it was concluded inter alia that (i) of the total inorganic solids in the influent, only a small fraction (2.8–7.5%) is incorporated into the mixed liquor, (ii) most of the inorganics in the influent (mean 88%) and effluent (mean 98.5%) are in the dissolved form, the balance being particulate, and (iii) the influent and effluent inorganic dissolved solids concentrations are closely equal (mean effluent to influent ratio 100%). Further, a number of models were developed to quantify the mixed liquor inorganic, and, hence, total solids. From an evaluation of these models against the experimental data, it would appear that the best approach to model the incorporation of inorganics into the activated sludge mixed liquor is to follow the concepts and principles used to develop the existing models for organic materials. With this approach, reasonably close correlation between predicted and measured data for mixed liquor and effluent inorganic concentrations were obtained.     

Design of Settlement Tanks and the use of Chemicals to Aid Precipitation of Suspended Solids

Traditionally, the design of settlement tanks has been based on practical experience linked to key criteria, which have evolved from many sources. In this paper, the design criteria which affect the performance of both primary and secondary tanks are examined and a procedure, linked to critical velocities and loading rates, is put forward to enable the design requirements to be rationalized.
Based on the authors' considerable practical experience, the proposed procedure can be used with confidence to design tanks which will achieve required performance, particularly in the case of secondary tanks (for separation of both activated and humus sludges). In particular, the importance of a correctly sized inlet stilling chamber, to reduce the feed velocity to around 0.003–0.005 m/s is explained.
The use of chemicals to aid removal of suspended solids (and hence BOD) has been practised for many years. Today, there is renewed interest, particularly for phosphate removal and for the treatment of some industrial wastewaters. The composition and nature of sewage affects the potential benefits of coagulant chemicals when added at the treatment works' inlet. The introduction of organic polymers has significantly improved performance and reduced costs. The major disadvantage of using chemicals relates to the significant increase in quantity of sludge that is produced, which will require both treatment and disposal, increasing operational costs.     

A solid chemical oxygen demand (COD) method for determining biomass in waste waters

A method of biomass determination similar to volatile suspended solids (VSS) that used chemical oxygen demand (COD) as a detection method instead of gravimetric methods is described. The “solid COD” method has a strong correlation with VSS for biomass at different stages of growth on different wastewaters including municipal sewage and bleached kraft mill effluent. Soluble COD from the wastewaters did not interfere with the assay. However, non-biomass suspended solids in chemi-thermo-mechanical pulping effluent were found to have a different COD/VSS ratio and thus interfered with solid COD results. The ratio between COD and VSS for biomass was approx. 1.2–1.6 mg COD/mg VSS.     

Grey-box modelling of aeration tank settling

A model of the concentrations of suspended solids (SS) in the aeration tanks and in the effluent from these during Aeration tank settling (ATS) operation is established. The model is based on simple SS mass balances, a model of the sludge settling and a simple model of how the SS concentration in the effluent from the aeration tanks depends on the actual concentrations in the tanks and the sludge blanket depth. The model is formulated in continuous time by means of stochastic differential equations with discrete-time observations. The parameters of the model are estimated using a maximum likelihood method from data from an alternating BioDenipho waste water treatment plant (WWTP). The model is an important tool for analyzing ATS operation and for selecting the appropriate control actions during ATS, as the model can be used to predict the SS amounts in the aeration tanks as well as in the effluent from the aeration tanks.     

Characterisation of pollutants washed off from road surfaces during wet weather

This paper presents the results of a monitoring programme carried out to study the washoff of various pollutants from impermeable road surfaces by the runoff produced under artificial and real rainfall conditions. Among the pollution parameters analysed are solids (total, suspended and total volatile), COD (chemical oxygen demand), ammonium and heavy metals (lead, copper, zinc and iron). Analysis of the results indicates a linear relationship between the mass loading rate of total solids, volatile solids and COD. The effect of runoff rate on the magnitude of pollution washed off has also been investigated. Particle size analysis, of the washoff solids shows that the predominant size fraction is < 50 μm. The average diameter of solids has been found to increase with an increase in the runoff rate.