Municipal wastewater treatment and biomass accumulation with a wastewater-born and settleable algal-bacterial culture

A wastewater-born and settleable algal-bacterial culture, cultivated in a stirred tank photobioreactor under lab conditions, was used to remove the carbon and nutrients in municipal wastewater and accumulate biomass simultaneously. The algal-bacterial culture showed good settleable property and could totally settle down over 20 min, resulting in a reduction of total suspended solids from an initial 1.84 to 0.016 g/l. The average removal efficiencies of chemical oxygen demand, total kjeldahl nitrogen and phosphate were 98.2 ± 1.3%, 88.3 ± 1.6% and 64.8 ± 1.0% within 8 days, respectively, while the average biomass productivity was 10.9 ± 1.1 g/m²·d. Accumulation into biomass, identified as the main nitrogen and phosphorus removal mechanism, accounted for 44.9 ± 0.4% and 61.6 ± 0.5% of total inlet nitrogen and phosphorus, respectively. Microscopic analysis showed the main algae species in the bioreactor were filamentous blue-green algae. Furthermore, denaturing gradient gel electrophoresis and 16S rDNA gene sequencing revealed that the main bacteria present in the photobioreactor were consortia with sequences similar to those of Flavobacteria, Gammaproteobacteria, Bacteroidia and Betaproteobacteria. This study explores a better understanding of an algae-bacteria system and offers new information on further usage of biomass accumulated during treatment.     

Enteric virus survival in algal-bacterial wastewater treatment systems—I : Laboratory studies

The survival of a representative enteric virus, poliovirus type 1, in laboratory models of algal-bacterial sewage treatment systems and the interactions of poliovirus with stabilization pond water was studied. In laboratory reactors a fraction of the total poliovirus present rapidly adsorbed to stabilization pond water solids by a reversible process, conforming to a Freundlich adsorption isotherm. In laboratory cultures the growth of Scenedesmus quadricauda and Bacillus megaterium in sterile sewage had no detrimental effect on poliovirus survival, whereas the growth of heterogeneous populations of stabilization pond bacteria in the same medium resulted in substantial virus inactivation. Appreciable poliovirus inactivation occurred in laboratory cultures of mixed algal-bacterial populations obtained from stabilization ponds. Because the degree of antiviral activity in these cultures was greater than that in cultures of stabilization pond bacteria alone, additional microbial factors must contribute to this virus inactivating phenomenon. The results of this study suggest that in algal-bacterial treatment systems both virus adsorption to solids and virus inactivation due to microbial activity play a role in reducing the enteric virus concentration in wastewater.     

Particulate-biofilm, expanded-bed technology for high-rate, low-cost wastewater treatment: nitrification

The performance of a particulate-biofilm, expanded-bed process for nitrification of activated sludge final effluent (ASFE) is reported for a plant receiving mixed industrial and domestic wastewater. The support material for the particulate-biofilms was glassy coke, to which the nitrifying bacteria attached and formed a highly active biofilm. An average nitrification rate of 1.7+/-0.6 kg m(expanded bed)(-3)d(-1) was recorded during operation of the bioreactor, which had a hydraulic residence time of 15 min. On average, the ASFE contained 12.6+/-3.7 g m(-3) NH3-N, which was reduced to 2.6+/-3.3 g m(-3) NH3-N. Furthermore, transfer of 10-12% of the oxygen in air was achieved using counter-current aeration. This investigation has demonstrated that a high rate of nitrification can be achieved with a particulate-biofilm, expanded-bed process. It has also demonstrated that the process can operate without backwashing and still remove particulate material from the ASFE feed.     

Operation of a deep, well-mixed, high-rate photosynthetic oxidation pond

The maximum depth for the stable operation of a photosynthetic high-rate oxidation pond was found to be 90cm. At this depth, both the pH and the peak oxygen concentration were significantly lower than the values obtained in shallow high-rate oxidation ponds.     

A mathematical model of a high sulphate wastewater anaerobic treatment system.

As an aid to the design and operation of anaerobic digesters treating high sulphate waste waters, a mathematical model describing this treatment process has been developed. Apart from sulphate reduction, the model includes those reactions which occur either prior to sulphate reduction or in competition with it. These include, hydrolysis of solid substrates, acidogenesis. beta oxidation of long chain fatty acids, acetogenesis and methanogenesis. By incorporating terms for these reactions the model is able to simulate sulphate reduction using a wide range of carbon sources. Acid/base equilibrium chemistry is included in order to predict the pH and unionized component concentrations, needed for calculating inhibition. An activity based model is used, with the activity coefficients calculated using Debye-Hückle theory. The mass transfer rates of hydrogen, methane, carbon dioxide and hydrogen sulphide from the liquid to the vapour phase are also included. A number of different reactor types may be simulated, including a dynamic batch. steady state CSTR and dynamic CSTR. By separating the hydraulic and solids residence times, high rate reactors such as UASB and packed bed reactors may also be simulated. The model has been used to successfully predict the dynamic and steady state behaviour of a number of different reactor types, utilizing both simple and complex carbon sources.     

矿山废水处理技术现状

阐述了矿井废水处理及利用的现状,针对煤矿废水的水质特征,介绍了高悬浮物、高矿化度、酸性废水、含重金属、含微有机物这五类煤矿废水的处理工艺技术,以期为煤矿废水的处理研究提供参考借鉴。     

海沧污水厂沉淀池上浮治理探析

本文对海沧污水厂沉淀池上浮的原因进行了分析,并针对性的采取降水、灌浆、增设底板附加层及进行池壁防渗等治理措施,使沉淀池上浮及时得到有效治理。     

A continuous Leontief dynamic input-output model

This paper extends the Leontief dynamic input-output model by incorporating continuous lags, capacity constraints, excess capacity and limits on disinvestment in each sector. These extensions result in phase changes, where sectors discretely change from one set of conditions to another. The resulting system of equations is solved by numerical methods and applied to the U.S. economy. Projections for the 1952 to 1962 period are compared with actual levels.     

辅助曝气式新型人工湿地模型处理污水的研究

人工湿地系统具有投资少、运行费用低、管理简单、处理效果稳定、便于就地回用等特点.在人工湿地的基础上增加曝气装置,推动了系统对COD的去除作用以及氨氮的硝化作用.研究表明,在进水COD为324mg/L、NH4＋-N为34mg/L的条件下,出水平均浓度分别为25,3.8mg/L,达到了国家一级A标准.     

A compartmental model to describe hydraulics in a full-scale waste stabilization pond

The advancement of experimental and computational resources has facilitated the use of computational fluid dynamics (CFD) models as a predictive tool for mixing behaviour in full-scale waste stabilization pond systems. However, in view of combining hydraulic behaviour with a biokinetic process model, the computational load is still too high for practical use. This contribution presents a method that uses a validated CFD model with tracer experiments as a platform for the development of a simpler compartmental model (CM) to describe the hydraulics in a full-scale maturation pond (7 ha) of a waste stabilization ponds complex in Cuenca (Ecuador). 3D CFD models were validated with experimental data from pulse tracer experiments, showing a sufficient agreement. Based on the CFD model results, a number of compartments were selected considering the turbulence characteristics of the flow, the residence time distribution (RTD) curves and the dominant velocity component at different pond locations. The arrangement of compartments based on the introduction of recirculation flow rate between adjacent compartments, which in turn is dependent on the turbulence diffusion coefficient, is illustrated. Simulated RTD’s from a systemic tanks-in-series (TIS) model and the developed CM were compared. The TIS was unable to capture the measured RTD, whereas the CM predicted convincingly the peaks and lags of the tracer experiment using only a minimal fraction of the computational demand of the CFD model. Finally, a biokinetic model was coupled to both approaches demonstrating the impact an insufficient hydraulic model can have on the outcome of a modelling exercise. TIS and CM showed drastic differences in the output loads implying that the CM approach is to be used when modelling the biological performance of the full-scale system.     

A model for the dynamic response of a cooling coil

The purpose of this study is to develop and evaluate simulation models for the dynamic performance of dry and wet cooling coils. The energy consumed by a building air conditioning system is directly related to that in the cooling coil. A dry-area model without consideration of condensation is established with three energy equations, and a wet-area model is developed based on a mass balance equation for moist air and three energy equations for the air, tube/fin, and working fluid. The derivatives with respect to the time variable are approximated using an explicit method, and the upwind approximation is used for the spatial variables. The results of the dry-area model show good agreement with those for the effectiveness method and the dynamic responses have reasonable physical meaning. The wet-area model is first compared to the dry-area model, and then the wet conditions are applied. A new factor called the mass transfer efficiency as a parallel to the total fin efficiency is introduced in the mass balance equation for the wet-area model to produce consistent results. The dynamic responses for several practical operations related to changing inlet conditions are reported. Comparisons indicate that the model predictions show good agreement with experimental data.     

A dynamic competition model for construction contractors

In construction, the issue of competition has been studied focusing on competitive bidding. The objective of most competitive bidding models is to find the optimum mark‐up to maximise the expected profit from a single firm's perspective. However, a firm's success depends on its long‐term interactions with the market and its competitors. To better understand competition in the market, there is a need to analyse competition from a dynamic market perspective. Building on previous models and relevant competition studies, a dynamic simulation model has been developed to provide an analytical framework for understanding dynamic competition. In this model, similar firms are equally exposed to demand uncertainties. Each applies its own policy, responding to market changes and to competitors' actions to optimise its market position. The firms' responses and their dynamic feedback are simulated and analysed. The results show how difficult it is for any firm to acquire a long‐term competitive advantage by means of bidding/marketing strategies—just as it is in the real world of price‐competitive contracting. Some considerations are presented for a single firm to develop a competitive strategy.     

Experimental validation of thermal model of open roof pond

This note presents a simple periodic thermal model for the performance of an open roof pond. The results of this model are seen to be in good agreement with experiment.     

A review of the technological feasibility of aquacultures for municipal wastewater treatment

The technical feasibility of utilising aquacultures for municipal wastewater treatment is reviewed. Aquacultures containing one or more aquatic weeds are cost effective for secondary and tertiary wastewater treatment, compared to the highly energy intensive conventional secondary and tertiary wastewater treatment systems. The major advantages are less capital and maintenance costs required as opposed to conventional wastewater treatment. Aquatic treatment systems utilising one or two aquatic weeds are efficient in substantial removal of phosphorus and nitrogen from the wastewater compared to the conventional secondary and tertiary wastewater treatment systems. Further, biogas generated from the harvested aquatic weed biomass could meet the treatment costs of the aquatic treatment systems utilising these aquatic weeds. Year round treatment of municipal wastewater utilising these aquatic weeds is possible even in the temperate regions of the world by housing the treatment systems in green houses. Other aquatic weeds which have tolerance to extreme cold conditions could be tested to make year round treatment of wastewater in aquatic treatment systems.     

废水生物处理中细胞生长动力学模型及其运用

从细胞生长的Monod方程式出发,讨论了基于Monod方程的细胞生长动力学在废水生物处理过程模拟中的修正、拓展,对废水生物处理过程模拟中Monod方程的运用进行了梳理。     

A probability model for investigating the trend of structural deterioration of wastewater pipelines

Canada’s infrastructure is aging and deteriorating. New legislation requires the municipalities to estimate operating and capital expenditures for running the systems into the future and to develop financial sustainability plans. Wastewater pipelines deterioration is currently not well understood and realistic deterioration models need to be developed.This paper demonstrates how the condition assessment data from trenchless visual inspections of wastewater pipelines can be used to understand the performance of wastewater pipelines. A new ordinal regression model for the deterioration of wastewater pipelines based on cumulative logits is elaborated. The model is presented using the Generalized Linear model formulation and takes into account the interaction effect between the explanatory variables. The new model is demonstrated and validated using the City of Niagara Falls high quality wastewater collection network condition assessment data for reinforced concrete (RC) and vitrified clay (VC) pipes.This new model is found to represent the City of Niagara Falls RC and VC pipes’ deterioration behavior for pipes in service for up to 110 years. RC pipes deterioration is found to be age dependent while VC pipes deterioration is not age dependent. This finding is contrary to other deterioration model studies that indicate that VC deterioration is age dependent. The service life for RC pipes is estimated to be approximately 75 years while VC pipes are found to have an indefinite service life if installed without structural damage.The cumulative logit model can be used to determine wastewater pipelines’ service life, predict future condition states, and estimate networks’ maintenance and rehabilitation expenditures. The latter is critical if realistic wastewater networks’ future maintenance and operation budgets are to be developed for the life of assets and to meet new regulatory reporting requirements. Further research is required to validate this new methodology for other networks and the deterioration modeling of pipe materials other than RC and VC.     

A neural network model to predict the wastewater inflow incorporating rainfall events

Under steady-state conditions, a wastewater treatment plant usually has a satisfactory performance because these conditions are similar to design conditions. However, load variations constitute a large portion of the operating life of a treatment facility and most of the observed problems in complying with permit requirements occur during these load transients. During storm events upsets to the different physical and biological processes may take place in a wastewater treatment plant, and therefore, the ability to predict the hydraulic load to a treatment facility during such events is very beneficial for the optimization of the treatment process. Most of the hydrologic and hydraulic models describing sewage collection systems are deterministic. Such models require detailed knowledge of the system and usually rely on a large number of parameters, some of which are uncertain or difficult to determine. Presented in this paper, an artificial neural network (ANN) model that is used to make short-term predictions of wastewater inflow rate that enters the Gold Bar Wastewater Treatment Plant (GBWWTP), the largest plant in the Edmonton area (Alberta, Canada). The neural model uses rainfall data, observed in the collection system discharging to the plant, as inputs. The building process of the model was conducted in a systematic way that allowed the identification of a parsimonious model that is able to learn (and not memorize) from past data and generalize very well to unseen data that was used to validate the model. The neural network model gave excellent results. The potential of using the model as part of a real-time process control system is also discussed.