Real-Time Detection of Sanitary Sewer Overflows Using Neural Networks and Time Series Analysis

Sanitary sewer overflows (SSOs) are becoming of increasing concern as a health risk. Utilities and regulators have taken preventive measures but many overflows still occur and are not identifiable, especially in access-challenged locations. Several mathematical approaches are presented for detecting if a disruption in the system is impending or occurring based on measurements at one or more locations in the system. Time series analysis and neural networks are used as prediction tools for expected depths and flows for single measurement locations and a neural network is developed for a multiple monitor system. Control limit theory is applied in all cases for identifying significant deviations of measured values from the expected values that suggest a SSO is occurring. Data from Pima County Wastewater Management’s monitoring system are used in two case studies.     

Electrochemical Pretreatment of Wastewater from Color Photograph Processing Unit

Wastewater emanating from color photograph processing units is usually in small quantities (5–20 L per day) and contains high concentrations of recalcitrant organic compounds. Disposal of such highly recalcitrant wastewater into a public sewer may result in an inhibiting effect on biological treatment system of a sewage treatment plant and thus these persistent organics can escape to receiving water bodies. A continuous full-scale treatment unit for such a small quantity of wastewater is not a viable option, economically and technically. In this study, a small batch type of an electrochemical reactor has been utilized to investigate the feasibility of electrochemical treatment of wastewater from a color photograph processing unit. The treatability studies were conducted using cast iron electrode. It was found that the cast iron electrode was efficient in removing both chemical oxygen demand and biochemical oxygen demand to the levels that meet the standards for discharge to surface water and public sewer. The energy consumption to meet the standards for sewer disposal was less compared to that of surface water disposal. The electrochemical reactor was found to be cost effective in both installation and operation for meeting the sewer disposal standards. It was concluded that the wastewater could be partially treated (pretreatment) electrochemically to meet the standard for sewer disposal rather than that of surface water disposal.     

Water consumption and wastewater discharge in China’s steel industry

China’s steel industry is one of the major water consuming and wastewater discharge-producing industries. Based on a water flow model, this study provides reasonable and clear definitions of water usage indexes for steel production. Using a survey of key producers, the status and problems of water consumption and wastewater discharge in Chinese steel industry are analyzed. The developments of water conservation and emission reduction are divided into three different stages, and present a slide decreasing curve. At the process level, coking is the heaviest pollution unit, while ironmaking and steelmaking are key parts of water consumption. Although the water resource efficiency has been significantly improved, the water usage level of key producers in China has exceeded the average world steel level; however, it is still lower than other advanced countries. Therefore, some measures and recommendations need to be implemented for Chinese steel industry to save water and reduce emissions.     

Influence of Wastewater Constituents on Hydrogen Sulfide Emission in Sewer Networks

Transport of wastewater in sewer networks causes potential problems associated with hydrogen sulfide in regard to odor nuisance, health risk, and microbially induced corrosion. To what extent these problems occur depends not only on the rate of sulfide formation but also on the rate of hydrogen sulfide emission into the sewer atmosphere. To gain understanding of the influence of wastewater constituents on the emission process, a number of batch experiments were conducted on domestic wastewater collected from sewer networks. The emission rate of hydrogen sulfide in the wastewater investigated was found to be approximately 60% of that in de-ionized water in terms of the overall mass-transfer coefficient, resulting in a correction factor (alpha) of 0.6. The alpha factor did not change significantly within the turbulence range studied (Froude numbers of 0.04–0.23). The Henry’s law constant for hydrogen sulfide in wastewater was observed to be close to that in de-ionized water, reflecting a correction factor (beta) of 1.0. By taking these results into account, modeling aspects of hydrogen sulfide emission in sewer networks are presented in this paper.     

Design of Sewer Line

Sewerage involves the major portion of the cost of a wastewater system. In the design of a sewerage system the sewer line is the basic unit occurring repeatedly in the design process. Any savings during the design of this unit will affect the overall cost of the sewerage system. A survey of the literature showed that the present status of sewer line design algorithms use linear programming and dynamic programming. The linear programming, using piecewise linearization of the objective function and constraints in every cycle, requires substantial computer time. On the other hand, dynamic programming algorithms are subjected to the “curse of dimensionality,” thus requiring large amounts of computer memory. In this paper, using a dimensionally consistent resistance equation, the sewer line design problem is formulated as a minimization of the cost function subjected to tight and loose constraints. The problem is solved by iterative application of the Lagrange-multiplier method.     

Optimal Distribution and Control of Storage Tank to Mitigate the Impact of New Developments on Receiving Water Quality

Storage tanks are commonly installed in a combined sewer system to control the discharge of combined sewer overflows that have been identified as a leading source for receiving water pollution. The traditional approach to determine the distribution of storage tank volume in the sewer system is confined to the use of objectives within the system itself due to the limits of separate modeling of urban wastewater systems, consisting of the sewer system, wastewater-treatment plant, and receiving water. The aim of this study is to investigate the optimal distribution and control of storage tanks with an objective to mitigate the impact of new residential development on receiving water quality from an integrated modeling perspective. An integrated urban wastewater model has been used to test three optimization scenarios: optimal flow rate control, storage distribution, and a combination of these two. In addition to the cost of storage tank construction, two receiving water quality indicators, dissolved oxygen and ammonium concentration, are used as optimization objectives. Results show the benefits of direct evaluation of receiving water quality impact in the context of storage distribution optimization. Results indicate that storage allocation should be considered in conjunction with optimal flow rate control to achieve the maximum effectiveness in water pollution mitigation.     

Modeling Ventilation Phenomenon in Sanitary Sewer Systems: A System Theoretic Approach

Municipal wastewater collection systems, due to the nature of their functions, carry varying concentrations of odorous gases. The production rate and transport of these gases within and out of sewer systems depend on air flow rate in the system piping. However, municipal sewers are generally designed to only transport sewage flow without giving consideration to the air flow field. As a consequence, the movement of air into, along, and out of collection systems is for the most part uncontrolled. The purpose of this paper therefore is to provide a new design protocol based on system theoretic techniques to be used by municipal engineers and environmentalists involved in odor control and sewer foul air transport studies. The modeling formulation accounts for combined wastewater drag and pressure-induced air flows, and manhole pressurization. The developed framework is applied to both hypothetical and real sewer systems to only illustrate the applicability of the modeling formulation.     

Ferrous Salt Demand for Sulfide Control in Rising Main Sewers: Tests on a Laboratory-Scale Sewer System

The addition of ferrous salts is a commonly used strategy for sulfide control in sewer networks. The Fe2+ dosing requirement in rising main sewers which takes into account of the effect of anaerobic sewer biofilms on the dosing demand is investigated. A laboratory-scale rising main sewer, consisting of four biofilm reactors in series and fed with real sewage, was operated for over 12 months, during which FeCl2 was dosed at several locations and at various dosing rates. The experimental results consistently revealed that approximately 0.7 mol of Fe2+ was required to precipitate sulfide formed from the reduction of 1 mol of sulfate by anaerobic sewer biofilms. This ratio is significantly lower than the ratio expected from reaction stoichiometry (molar ratio of 1:1), and also the Fe2+ to sulfide ratio (1.07–1.10 mol:1 mol) observed in batch tests conducted with real wastewater in the absence of sewer biofilms. Biofilms adapted to Fe2+ addition were found to contain a substantially higher amount of elemental sulfur than biofilms not receiving Fe2+ dosage. This suggests Fe2+ addition might have altered the final product of sulfate reduction by anaerobic sewer biofilms. The study also showed that the addition of ferrous salts at the inlet of a rising main sewer can effectively control sulfide throughout the whole system despite of the presence of competing anions in wastewater. Phosphate precipitation with ferrous iron in anaerobic rising main sewers is negligible.     

Gas-Liquid Mass Transfer along Small Sewer Reaches

Municipal and industrial sewers may be localized sources of volatile organic compound (VOC) emissions to the ambient atmosphere. Previous studies of VOC emissions from sewers have focused on sewers with large diameters that are often characterized as having mild channel slopes and as conveying relatively large wastewater flow rates. The study described in this paper was completed to better understand VOC emissions from sewer reaches with small diameters, steep channel slopes, and relatively low wastewater flow rates (e.g., as might be typical for building laterals, street sewers, and on-site industrial sewers). Mathematical models were developed to investigate the nature of mass transfer kinetics and equilibrium conditions in such sewers. A series of 20 experiments were then completed to determine liquid-phase and gas-phase mass transfer coefficients for a range of sewer operating conditions and chemical properties. Experiments were completed in an experimental sewer reach (60 m length, 0.2 m diameter) using five volatile chemicals (acetone, ethyl acetate, toluene, ethylbenzene, and cyclohexane, listed in order of increasing Henry's law constants). Experimental stripping efficiencies were as high as 47% for cyclohexane and as low as 0.3% for acetone. Experimental and mathematical results indicate that VOCs with low Henry's law constants (e.g., acetone) can reach equilibrium conditions rapidly in sewers. However, emissions of VOCs with high Henry's law constants (e.g., cyclohexane) are kinetically limited, allowing for the sewer to be treated as an “open” system. The findings described herein suggest that a large fraction of VOCs with high Henry's law constants may be emitted to the ambient atmosphere in the near vicinity to the point of discharge.     

Propagation of Waves and Dissolved Compounds in Sewer

The phenomenon of the surface wave propagating faster than the fluid that induced it is studied experimentally and numerically. The study focuses on the importance of the wave phenomenon for the urban hydrology system, where it can determine the impact of combined sewer overflows on the environment and the operation of a novel urine (anthropogenic nutrient solution) separation system. Urine would be stored decentrally and released during the night hours so that a wave would form in the sewer. The full-scale experiments were carried out in a 2-km section of a main sewer. The wave was induced with the aid of fire hydrant water traced by salt. Five measurements and sampling stations were operated downstream through which the transport of both fluid and compounds were analyzed. Numerical simulations of the results are discussed focusing on the reliability of friction approaches and dispersion prediction. Although difficult to model with commercial tools, it was shown that the wave phenomenon has no adverse effects on the practicability of the urine separation system, but can lead to the release of undiluted wastewater during a rain event.     

Application of Cross-Flow Microfiltration for the Treatment of Combined Sewer Overflow Wastewater

Application of cross-flow microfiltration with and without backpulsing is evaluated for the treatment of dilute primary sewage effluent simulating combined sewer overflow wastewater. Four alpha alumina ceramic membranes of various pores sizes (0.2–5.0?μm) were tested to understand the impact of cross-flow velocity and transmembrane pressure on the permeate water quality and flux rate. The 0.2 and 0.8?μm membranes produced a permeate water quality that is likely to be suitable for surface water discharge. The combination of permeate chemical and biological water quality and long-term flux rates suggest that a 0.2?μm membrane would be the most appropriate membrane for the treatment of combined sewer overflow wastewater within sewersheds.     

我国有色金属冶炼行业废水污染防治的现状与对策

我国是有色金属生产大国。有色金属冶炼过程中产生的工业废水对环境带来了极大危害。为了不断加大对有色金属冶炼行业水污染的监管力度，我国出台了一系列法规政策。在技术层面，大多数有色金属冶炼企业通过化学、物理或生物的方法进行废水处理，基本实现了废水达标排放的目标。但是冶炼行业环境污染问题仍然突出，污染事故也时常发生。未来，尚需要在源头减污、过程控制、末端治理等方面着力，不断提升有色金属冶炼行业的废水污染防治水平，助力生态环境的改善。     

国家新钢铁工业水污染物排放标准浅析

分析了国家钢铁工业水污染物排放标准征求意见稿的特点,包括降低了主要污染物的排放限值、取消了按废水去向分级管理的规定、增加了部分污染物排放控制项目、规定了各类污染物排放监控位置等。新标准能够促进钢铁行业结构调整,促进节能减排,实现经济发展和环境保护的双赢。     

Bacteria Load Estimator Spreadsheet Tool for Modeling Spatial Escherichia coli Loads to an Urban Bayou

The model developed in this paper, the bacteria loading estimator spreadsheet tool (BLEST), was designed as an easy to use indicator bacteria model that can overcome the shortcomings of many of the simpler total maximum daily load (TMDL) modeling approaches by integrating spatial variation into load estimates. BLEST was applied to the Buffalo Bayou watershed in Houston, Texas and incorporated loading from point and nonpoint sources, such as wastewater treatment plants, sanitary sewer overflows, septic systems, storm sewer leaks, runoff, bed sediment resuspension, and direct deposition. The dry weather Escherichia coli load in Buffalo Bayou was estimated using BLEST to be 244 billion MPN/day and would require an overall 48% reduction to meet the contact recreation standard, while wet weather loads would need to be reduced by 99.7%. Dry weather loads were primarily caused by animal direct deposition, septic systems and discharges from storm sewers under dry weather conditions, while wet weather loads were mostly attributable to runoff and resuspension from sediment. Unlike most simple TMDL load allocation strategies, BLEST can be used to evaluate spatially variable load reduction strategies. For example, septic system load reductions implemented in less than 10% of the subwatersheds resulted in a decrease in bayou loading of more than 20%.     

Infrastructure Condition Prediction Models for Sustainable Sewer Pipelines

The Federation of Canadian Municipalities reported that approximately 55% of sewer infrastructure in Canada did not meet current standards. Therefore, the burden on Canadian municipalities to maintain and prioritize sewers is increasing. One of the major challenges is to develop a framework to standardize the condition assessment procedures for sewer pipelines. Lack of detailed knowledge on the condition of sewer networks escalates vulnerability to catastrophic failures. This research presents a proactive methodology of assessing the existing condition of sewers by considering various physical, environmental, and operational influence factors. Based on historic data collected from two municipalities in Canada, structural and operational condition assessment models for sewers are developed using the multiple regression technique. The developed regression models show 82 to 86% accuracy when they are applied to the validation data set. These models are utilized to generate deterioration curves for concrete, asbestos cement, and polyvinyl chloride sewers in relation to traffic loads, bedding materials, and other pipe characteristics. The developed models are expected to assist municipal engineers in identifying critical sewers, prioritizing sewer inspections, and rehabilitation requirements.     

Sewer-Sediment Control: Overview of an Environmental Protection Agency Wet-Weather Flow Research Program

This paper presents a historical overview of the sewer sediment control projects conducted by the Wet-Weather Flow Research Program of the United States Environmental Protection Agency. The research presented includes studies of the causes of sewer solids deposition and development/evaluation of control methods that can prevent sewer-sediment accumulation. Discussions focus on the relationship of wastewater characteristics to flow-carrying velocity, abatement of solids deposition and solids resuspension in sewers, and sewerline flushing systems for removal of sewer sediment. Methods for abating sewer sedimentation include steeper sewer slope, pipe bottom shapes that maintain high velocity during low-flow conditions, and periodic sewer flushing. The future research program plan for sewer-sediment control is also presented.     

Optimization Modeling for Sewer Network Management

Due to their low visibility, sanitary sewers' condition assessment and rehabilitation are frequently neglected until a catastrophic failure occurs. Neglecting regular maintenance of these underground utilities adds to life-cycle costs and liabilities, and in extreme cases causes stoppage or reduction of vital services. A systematic approach for the determination of deterioration of sewer systems and an integrated management system are necessary to fully understand the complete status of this underground infrastructure system. This paper discusses the major aspects of integrated management for sewer systems, namely, the development of network identification, sewer classification and sewer condition rating systems, sewer deterioration mechanisms, prediction modeling, and the use of optimization techniques for maximizing benefit∕cost ratios over a planning horizon. A case study, based on large combined sewers from the city of Indianapolis, has been used to demonstrate the use of the framework of this integrated life-cycle based sewer management system. Deterministic dynamic programming is employed to identify appropriate sewer rehabilitation techniques at different stages during the planning horizon adopted for the sewer systems.     

加快钢管标准体系建设 促进钢管行业结构调整

从产能、产量、装备水平、品种开发和企业盈利能力等方面出发,分析了我国钢管行业的现状;介绍了我国钢管标准体系建设取得的成绩。指出应加快钢管标准体系建设,促进钢管行业结构调整和淘汰落后,保持行业健康可持续发展。     

钢铁企业污水深度处理后浓盐水处理实践

随着污水深度处理在钢铁企业的广泛应用,浓盐水合理处理已成为钢铁企业污水深度处理的关键环节。以某钢铁企业浓盐水处理为例,针对原水水质指标和浓盐水控制标准,设计了浓盐水处理工艺流程,介绍了各单元处理原理和作用。通过实际运行,详细分析了对化学需氧量(COD)、氨氮和总氮的处理效果,浓盐水经处理后可以达到《钢铁工业水污染物排放标准》(GB 13456—2012)中特别排放限值要求。一级脱盐浓水处理成本约为6元/m3,二级脱盐超浓水处理成本约为15元/m3。