Sewer Solids Research Articles

Effects of temperature and dissolved oxygen on hydrolysis of sewer solids

Effects of temperature and dissolved oxygen (DO) on kinetics of microbial transformation processes of suspended sewer sediment particles, suspended wastewater particles and wastewater were investigated. Microbial activity was estimated by the oxygen uptake rate. The effects were studied under conditions where biomass had not acclimated to changed temperature or DO conditions. Hydrolysis processes limited the availability of organic substrates for the aerobic microbial growth. The effects of temperature were interpreted applying an Arrhenius relationship. The average Arrhenius constants found for sewer sediment particles and wastewater particles differed significantly from the average Arrhenius constant found for wastewater. The effects of dissolved oxygen concentration were interpreted applying a saturation type relationship. No differences between sewer sediment particles, wastewater particles and wastewater were found for the oxygen saturation coefficients.

Aerobic microbial transformations of resuspended sediments in combined sewers - a conceptual model

A methodology for characterisation and a concept for modelling of aerobic microbial transformations of resuspended sewer sediments based on long term measurements of oxygen utilisation rates (OUR's) are presented. The OUR measurements were evaluated applying a conceptual model for aerobic microbial transformations of sewer solids based on methodologies originating from description of activated sludge processes. Validation showed that yield coefficient and maximum growth rate could be considered constant when readily biodegradable substrate was added to the resuspended sewer solids during the OUR experiment. Maintenance energy requirement of the biomass was argued to be a better concept for modelling microbial transformations compared with either considering decay of biomass into hydrolysible substrate or including endogenous decay of biomass. OUR measurements are recommended as a valuable methodology for characterisation of suspended sewer sediments in terms of COD-fractions and related biotransformations.

Aerobic microbial transformations of resuspended sediments in combined sewers — A conceptual model

A methodology for characterisation and a concept for modelling of aerobic microbial transformations of resuspended sewer sediments based on long term measurements of oxygen utilisation rates (OUR's) are presented. The OUR measurements were evaluated applying a conceptual model for aerobic microbial transformations of sewer solids based on methodologies originating from description of activated sludge processes. Validation showed that yield coefficient and maximum growth rate could be considered constant when readily biodegradable substrate was added to the resuspended sewer solids during the OUR experiment. Maintenance energy requirement of the biomass was argued to be a better concept for modelling microbial transformations compared with either considering decay of biomass into hydrolysible substrate or including endogenous decay of biomass. OUR measurements are recommended as a valuable methodology for characterisation of suspended sewer sediments in terms of COD-fractions and related biotransformations.

The performance of a novel combined sewer overflow with perforated conical screen

Increasing concern over the discharge of sewer solids from combined sewer overflows (CSOs) has encouraged the introduction of installations which incorporate either mesh or bar screen arrangements, or both. Gross solids create visual and aesthetic pollution if they reach watercourses. An entirely new arrangement for a CSO with a perforated screen of 6 mm diameter apertures is described in the paper. The arrangement is circular, with tangential flow across the screen to facilitate its cleaning. High velocities across the screen holes ensure that solids which have been prevented from discharging are swept clear from the screen. As a result, a sufficient screen area remains free from trapped solids to permit discharge of flow. The device has been designed to meet all anticipated performance criteria for the removal of solids, and to require a minimum of maintenance. A thorough testing programme in different conditions is described. Laboratory testing utilised a wide range of gross solids and flows to determine efficiencies of solids removal under all anticipated operating conditions. The performance of the CSO in a sewer environment was evaluated at a sewage treatment works with flows up to 1801/s using both raw and treated sewage to simulate storm sewage of different strengths. Both the device and its testing are described, together with the results of the testing programme.

The performance of a novel combined sewer overflow with perforated conical screen

Increasing concern over the discharge of sewer solids from combined sewer overflows (CSOs) has encouraged the introduction of installations which incorporate either mesh or bar screen arrangements, or both. Gross solids create visual and aesthetic pollution if they reach watercourses. An entirely new arrangement for a CSO with a perforated screen of 6 mm diameter apertures is described in the paper. The arrangement is circular, with tangential flow across the screen to facilitate its cleaning. High velocities across the screen holes ensure that solids which have been prevented from discharging are swept clear from the screen. As a result, a sufficient screen area remains free from trapped solids to permit discharge of flow. The device has been designed to meet all anticipated performance criteria for the removal of solids, and to require a minimum of maintenance.A thorough testing programme in different conditions is described. Laboratory testing utilised a wide range of gross solids and flows to determine efficiencies of solids removal under all anticipated operating conditions. The performance of the CSO in a sewer environment was evaluated at a sewage treatment works with flows up to 1801/s using both raw and treated sewage to simulate storm sewage of different strengths. Both the device and its testing are described, together with the results of the testing programme.

Mechanics of sewer sediment erosion and transport

Knowledge about the behaviour and effects of solids in sewer systems has advanced considerably in the past decade, with new guidance for the control of sewer solids and associated pollutants emergi...

Summary: United States “sewer solids” settling characterization methods, results, uses and perspective

This paper summarizes recent U.S. experience involving “sewer solids” settling experiments. Over the last 15 years many such characterizations have been conducted during the design of combined sewer overflow (CSO) and stormwater high rate treatment facilities. Since the early 1980s there has been little organized U.S. research to summarize results and settling column methods used. This information is organized and solids settling curves for different waste types are presented noting settling column method used. Median settling velocities for each waste type are given.

Settleable sewer solids at stormwater tanks with clarifier for combined sewage

A six-year study of CSO problems showed that in most cases the settleable sewer solids are responsible for poor water quality. This is the reason why the settling behaviour of settleable solids should be taken into account at stormwater treatment to a greater degree than it is done up to now. New efficiency measurements at stormwater tanks with clarifier overflows for combined sewage showed two important results: 1) The annual mean surface loading qA of a clarifier-type CSO tank is only about 25 % of the design surface loading of 10 m3/(m·h) recommended by the German guideline A 128. 2) The settling process in stormwater tanks is effective: - The median settling velocity vs of sewer solids is reduced from about 0,21 cm/s to vs = 0,035 cm/s. - The concentration of settleable solids is reduced about 80 %, that of total solids about 65% and COD concentration about 50 %. With this efficiency, well designed stormwater tanks will be a good measure in many cases to reduce significantly CSO impacts on receiving water quality.

A study of WC derived sewer solids

Little is currently known about the nature, quantity or variability of WC derived sewer solids. This work describes results of a one week domestic WC usage survey in the UK. Specific attention is paid to solid production including faecal matter, toilet paper and sanitary refuse. Significant quantities of solids were found to be produced. The results illustrate distinctive diurnal usage patterns including the surprisingly low evening faecal related flush usage. Weekend usage exceeded week day usage on average, but with reduced morning peaks. Differences between males and females usage were also noted, in particular the much larger toilet paper usage and sanitary refuse disposal associated with females.

Summary: United States 'sewer solids" settling characterization methods, results, uses and perspective

This paper summarizes recent U.S. experience involving "sewer solids" settling experiments. Over the last 15 years many such characterizations have been conducted during the design of combined sewer overflow (CSO) and stormwater high rate treatment facilities. Since the early 1980s there has been little organized U.S. research to summarize results and settling column methods used. This information is organized and solids settling curves for different waste types are presented noting settling column method used. Median settling velocities for each waste type are given.

Settleable sewer solids at stormwater tanks with clarifier for combined sewage

A six-year study of CSO problems showed that in most cases the settleable sewer solids are responsible for poor water quality. This is the reason why the settling behaviour of settleable solids should be taken into account at stormwater treatment to a greater degree than it is done up to now. New efficiency measurements at stormwater tanks with clarifier overflows for combined sewage showed two important results:1)The annual mean surface loading qA of a clarifier-type CSO tank is only about 25 % of the design surface loading of 10 m3/m·h) recommended by the German guideline A 128.2)The settling process in stormwater tanks is effective:-The median settling velocity νvs of sewer solids is reduced from about 0,21 cm/s to νs = 0,035 cm/s.-The concentration of settleable solids is reduced about 80 %, that of total solids about 65% and COD concentration about 50 %.With this efficiency, well designed stormwater tanks will be a good measure in many cases to reduce signi ficantly CSO impacts on receiving water quality.

A study of WC derived sewer solids

Little is currently known about the nature, quantity or variability of WC derived sewer solids. This work describes results of a one week domestic WC usage survey in the UK. Specific attention is paid to solid production including faecal matter, toilet paper and sanitary refuse. Significant quantities of solids were found to be produced. The results illustrate distinctive diurnal usage patterns including the surprisingly low evening faecal related flush usage Weekend usage exceeded week day usage on average, but with reduced morning peaks. Differences between males and females usage were also noted, in particular the much larger toilet paper usage and sanitary refuse disposal associated with females.

International workshop on origin, occurrence and behaviour of sediments in sewer systems: Summary of conclusions

An international workshop held at the Université Libre de Bruxelles (4–6 Sept. 1991) on the “origin, occurrence and behaviour of sediments in sewer systems” has shown that much progress has been made in the last 5 years in the general understanding of sewer sediments. Comprehensive research programmes, including field surveys, have indicated that solids found in sewers, either in suspension or in deposition, cannot be considered as having a unique entity. On the basis of sewerage and sources, a categorization can be made between three broad types of solids: sewer grits, sanitary solids and (runoff-generated) fine material. Although some other categorizations are also possible, it is apparent that each of these three types has very specific physico-chemical characteristics and this has important implications both from the environmental and the operational points of view. The diversity of the types of sewer solids is not infinite (from place to place, sediments will differ only within relatively narrow bands), nonetheless the differences are the main reason why the development of a “universal” sewer sediment transport model is a remote prospect. For some elementary processes, such as the movement of non-cohesive grit in drainage conduits, detailed engineering solutions are beginning to emerge. It is also apparent that bed shear stress is a more appropriate parameter than flow velocity for defining erosive or depositional criteria in sewers. There is no doubt that in the future, the various problems of sewer sediments, washout of pollutants during storm overflows, reduction of hydraulic capacity, recurrent costs for cleaning sewerage lines and tanks, will have to be considered intrinsically in all urban drainage applications (design and analysis). It is also likely that wastewater treatment technology (and terminology) will intrude more and more in the apparent unchanging traditions of sewer network operation.

Report on European sewerage systems, with special reference to the needs of the city of Philadelphia

Sediments in sewers are ubiquitous because of the diverse nature of the inputs. Over the past decade or so, new understanding of the provenance, behaviour and nature of sewer solids is now allowing more effective means for solids management. Whilst current computer models are good at representing the hydraulic performance of sewer systems, their handling of sewer solids and associated processes is still embryonic. Hence any attempts to manage in-sewer solids more effectively require a diversity of approaches, both for any modelling studies and for the selection of the most appropriate option. Little information currently exists on which to draw to determine cost-effective or wholelife solutions. Nonetheless significant advances have been made in enhancing the traditional approaches to sewer solids management which have been in use for more than a century.