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p-Index From 2021 - 2026
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All Journal Civil Engineering Journal
Valentina Dimova
Sofiyska voda part of Veolia, 159 "Tsar Boris III" Blvd., Sofia 1618
Civil Engineering, Building, Construction & Architecture

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High-Resolution Assessment of Wastewater Heat Recovery Potential for Urban Decarbonization Emil Tsanov; Galina Dimova; Ivelina Hinova; Viden Radovanov; Valentina Dimova
Civil Engineering Journal Vol. 12 No. 5 (2026): May
Publisher : Salehan Institute of Higher Education

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.28991/CEJ-2026-012-05-01

Abstract

This study assesses the technical potential for wastewater heat recovery in Sofia and its contribution to domestic hot water supply and greenhouse gas reduction. Heat extraction locations were identified using temperature and flow data from the sewer network and the municipal wastewater treatment plant (WWTP) Kubratovo. Temperature thresholds were defined to ensure stable biological treatment ( ≥ 10°C influent) and environmental protection ( ≥ 5°C effluent). Four scenarios were analyzed, considering heat recovery at the WWTP inlet and outlet with ΔT = 2–4 K. The heat recovery potential is evaluated using 15-minute temperature and flow data by applying scenario-specific temperature thresholds, enabling a dynamic assessment that captures real variations in both flow and temperature and explicitly accounts for system shutdown periods. Heat recovery at the WWTP effluent provides higher and more stable yields than at the influent. The potential ranges from 238,536–380,314 MWh/year at the inlet and 264,828–529,705 MWh/year at the outlet. Under the most favorable scenario (effluent, ΔT = 4 K), the recovered heat can supply domestic hot water to over 76,000 households, reducing emissions by more than 200,000 t CO₂/year when replacing natural gas.
Runoff Coefficient Variability in Green and Bitumen Roof Systems Emil Tsanov; Dobril Valchev; Irina Ribarova; Valentina Dimova
Civil Engineering Journal Vol. 12 No. 8 (2026): August
Publisher : Salehan Institute of Higher Education

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.28991/CEJ-2026-012-08-03

Abstract

This study aimed to generate field-based evidence supporting sustainable urban stormwater management under the continental climatic conditions. The runoff behavior of a retrofitted green roof was monitored and compared with that of an adjacent conventional bitumen roof of identical geometry. Monitoring was conducted from March 2022 to January 2024. A total of 34 rainfall events (3–74 mm) were analyzed to evaluate runoff coefficients (RC) and their relationships with precipitation depth, antecedent dry days (ADD), and rainfall duration. The average RC was 0.24 (0–0.84) for the green roof and 0.81 (0.43–1.00) for the bitumen roof. The green roof effectively retained rainfall events below approximately 10 mm and showed increasing runoff variability with increasing precipitation depth. A moderate relationship was observed between RC and ADD for the green roof (R² = 0.518), whereas no meaningful relationship was found for the bitumen roof. Rainfall duration had no significant effect on runoff generation. The findings confirm the considerable runoff reduction potential of extensive green roofs under continental climatic conditions and demonstrate that rainfall depth and antecedent moisture conditions are key controls of runoff response. The long-term field evidence generated in this study provides a sound basis for improving green roof design and sustainable stormwater management.
Co-Authors Dobril Valchev Emil Tsanov Emil Tsanov Galina Dimova Irina Ribarova Ivelina Hinova Viden Radovanov