Costs and optimisation options for monitoring of indirect dischargers

Monitoring of indirect and industrial dischargers, respectively, makes an important contribution to the safe and environmentally sound operation of wastewater systems. As a result of local framework conditions, there is a wide range of monitoring practices across Germany. In a benchmarking project, ten sewerage operators and monitoring bodies representing large German cities have collected data on their work and discussed their practices. The results show that the extent of monitoring is between 244 and 1,457 monitoring points per sewer network (given as 15th and 85th percentile). The median value of the specific expense is 689 EUR per monitoring point and year. In relation to the total wastewater fee volume, the median expense is 0.71%. The sub-process ‘sampling’ was examined more closely. By means of detailed process mapping and regression analyses, it can be shown that on-site activities and tours have the largest share of working time (total of 72%) and thus the greatest leverage in optimisation measures. Various examples are given.

Designing the sewerage network of the city in purpose to reduce impact to the environment and water bodies

Today, the study of the city’s sewerage network is an important part of the life of the city and the environment. Ensuring optimal living conditions not only for oneself, but also for other participants in the environment should be a priority for a person. Today we can face various problems that complicate the operation of the city sewer network and can cause detrimental effects on the environment. To prevent this impact on the environment, you first need to understand the cause of this impact, and then look for a solution. Wastewater is a pollutant of rivers, lakes and the water system in general. Wastewater is formed in connection with human activity, the appearance of rainwater, as well as under the influence of industrial enterprises. The purpose of the article is to develop the management of wastewater flows within the city sewer network to ensure the highest quality water clarification and minimize environmental harm.

Hydrodynamic assessment of object on the sewer network in the city of Trnava

As in most Slovak cities, there is a combined sewer network in the city of Trnava. Therefore, combined sewer overflow (CSO) must be provided on these networks in order to mix rainwater and sewage water. The purpose of these CSO’s is to reduce the amount of rainwater supplied to the treatment plant and to discharge part of the rainwater to the recipient. However, these waters contain various contaminants, including coarse solids, fine suspended solids, and solutes. Due to this, reduced water quality was recorded in the Trnávka recipient. This reduced quality is also due to the increased number of reliefs as prescribed by Government Regulation n.269/2010. The aim of the work is the analysis and selection of unsuitable relief chambers that do not meet the given limits. Hydrodynamic simulations are performed on these chambers, which demonstrate the need to reduce the amount of rainwater or reconstruction of CSO’s.

Evaluation of sewer network resilience index under the perspective of ground collapse prevention

Generally, when evaluating the resilience of infrastructure, the four properties of resilience robustness, rapidity, resources, and redundancy (4Rs) are widely considered. However, there is little research on the resilience assessment of sewer networks. Therefore, to establish a framework to evaluate sewer network resilience under the perspective of urban ground collapse prevention, this study considers the 13 second-level detailed indicators corresponding to the 4 first-level indicators (4Rs) based on literature reviews and experts' opinions. An analytic hierarchy process (AHP) is used to obtain relative weights of each indicator and a weighted sum method (WSM) is used to evaluate sewer network resilience index (SRI). The evaluation system was applied to 8 small blocks of selected drainage areas in Seoul, South Korea, and the SRI of 8 small blocks are computed. This study could help the sewer management department to make decisions and manage sewer network assets that enhance the resilience of the sewer networks.

Dissolved oxygen determination in sewers using flow hydraulic parameters as part of a physical simulation model

This paper aims to develop a model for calculating the hydraulic and water quality parameters of wastewater within sewers. Information from the wastewater collection network and the transmission line in Birjand were used to verify the model performance. The parameters used for modelling quality changes include the yield constant for biomass (YH), the maximum specific growth rate (μH), the saturation constant for dissolved oxygen (KOG) and the saturation constant for readily biodegradable substrate within a biofilm (KSF), as well as the Gauckler–Manning–Strickler coefficient (n). They were selected from references and were verified at the calibration stage comparing measurements with the modelling values. Inputs of the created model are the average concentrations of dissolved oxygen and chemical oxygen demand of the incoming wastewater, the flow rate of wastewater at the exit point of the network, physical characteristics of the pipes and the height of drops within the sewer network. The amount of dissolved oxygen at different positions of the sewer network was calculated. The acceptable calculated sum of squares of errors and the correlation coefficient (R2) of the calibrated model for dissolved oxygen were 1.6872 and 0.77, respectively.

Detection and quantification of SARS-CoV-2 RNA in wastewater influent in relation to reported COVID-19 incidence in Finland

Wastewater-based surveillance is a cost-effective concept for monitoring COVID-19 pandemics at a population level. Here, SARS-CoV-2 RNA was monitored from a total of 693 wastewater (WW) influent samples from 28 wastewater treatment plants (WWTP, N = 21–42 samples per WWTP) in Finland from August 2020 to May 2021, covering WW of ca. 3.3 million inhabitants (∼ 60% of the Finnish population). The relative quantity of SARS-CoV-2 RNA fragments in the 24h-composite samples was determined by using the ultrafiltration method followed by nucleic acid extraction and RT-qPCR assay targeted with N2-assay. SARS-CoV-2 RNA signals at each WWTP were compared over time to the numbers of new and confirmed COVID-19 cases in the sewer network area.Over the 10-month surveillance period, the detection rate of SARS-CoV-2 RNA in WW was 79% (including 6% uncertain results), while only 24% of all samples exhibited gene copy (GC) numbers above the quantification limit. The range of the SARS-CoV-2 detection rate in WW varied from 33% (including 10% uncertain results) in Pietarsaari to 100% in Espoo. Only six out of 693 WW samples were positive with SARS-COV-2 RNA when the reported COVID-19 case number from the preceding 14 days was zero. Overall, the 14-day COVID-19 incidence was 7, 18 and 36 cases within the sewer network area when the probability to detect SARS-CoV-2 RNA in wastewater samples was 50%, 75% and 95%, respectively. The quantification of SARS-CoV-2 GC required significantly more COVID-19 cases: the quantification rate was 50%, 75% and 95% when the 14-day incidence was 110, 152 and 223 COVID-19 cases, respectively, per 100 000 persons. Multiple linear regression confirmed the relationship between the COVID-19 incidence and the SARS-CoV-2 GC quantified in WW at 15 out of 28 WWTPs (overall R2 = 0.36, p < 0.001). At four of the 13 WWTPs where a significant relationship was not found, the GC of SARS-CoV-2 RNA remained below the quantification limit during the whole study period. In the five other WWTPs, the sewer coverage was less than 80% of the total population in the area and thus the COVID-19 cases may have been inhabitants from the areas not covered.Based on the results obtained, WW-based surveillance of SARS-CoV-2 could be used as an indicator for local and national COVID-19 incidence trends. Importantly, the determination of SARS-CoV-2 RNA fragments from WW is a powerful and non-invasive public health surveillance measure, independent of possible changes in the clinical testing strategies or in the willingness of individuals to be tested for COVID-19.

USE AND DISPOSAL OF ACIDIC WATER CONDENSATE FROM GAS-FIRED BOILER UNITS

During operation in boiler units of modern condensing boilers or modernization of old-style boilers, water condensate is formed due to heat-recovery equipment in the mode of cooling exhaust-gases below the dew point of water vapor. At natural gas is burned in equipment, the range of values of the pH value of the condensate is within the range of 3 ÷ 6. In this connection, the problem arises of the useful use of this condensate or its safe drainage into the sewer network. At useful use, the resulting condensate can be used for the needs of the boiler units (for washing boilers, in chemical water-purification systems) or outside the boiler house (for laundries, greenhouses, swimming pools, etc.). In the case of condensate drainage into the city sewer network, as a rule, its preliminary decarbonization is required. This is a necessary environmental measure and operational standard to protect the sewer network and related equipment, including treatment facilities, from premature wear. Among the directions of condensate decarbonization known in Ukraine, the most common are: - decarbonization by degassing by the contact method, which consists in removing CO2 from the heated solution by blowing air in the nozzle layer (ceramic or plastic), through which condensate flows. Degassing occurs due to the instability of the H2CO3 compound, which, when heated, easily decomposes into H2O and CO2; - chemical decarbonization, by combining carbon dioxide in an insoluble compound with various reagents, which are added to the container using a dispenser; - decarbonization by passing the condensate through a granular filter containing calcium carbonate, such as marble chips or lime. Removal of carbonic acid from condensate during filtration in a layer of marble chips is seen as the simplest method of decarbonization of water condensate from those considered. On the basis of this method of decarbonization, the authors propose a technical solution for the developed neutralizer with a description of its design and operating principle. The paper presents the results of calculated studies of the volumes of formed condensate and an example of its safe use in the case of modernization of a gas-fired water-heating boiler with a nominal thermal power of 1 MW by a heat-recovery system with simple or complex use of heat. It is shown that when using modern heat-recovery technologies in gas-fired boiler houses, there are different circuit and technical solutions for possible useful use or safe evacuation of acidic condensate formed during the implementation of these technologies. In cases where it is advisable to neutralize this condensate, there are effective methods for its decarbonization and appropriate equipment.