Iranian Journal of

Background and Objective: Dolochar is the residual ash from the production of sponge iron in the process of direct reduction of iron ore by the coal-based method. In Iran, this waste is transported to the nearest landfill. However, these methods are a major environmental concern due to the fineness of the waste and the presence of heavy metals in its composition. The aim of the present study is to investigate the methods of reusing dolochar in order to solve the environmental problem and further use it as auxiliary materials in applications such as road construction and wastewater treatment.
Materials and Methods: In depth investigation of the word “Dolochar” in Science Direct, SID, and MagIran databases showed that there is no long history of reusing it. Only 14 English articles were found, all of which were used in research; Therefore, the present article deals with the issue of reusing Dolochar in Iran for the first time.
Results: By reviewing previous studies, reuse of Dolochar has been classified into five sections. Dolochar use in wastewater treatment (removal of copper, chromium, paint, phosphate, nitrate, surfactant), removal of chromium from mine effluent (more than 94%), as a synthesis gas, as a filter medium (three times better than sand filters) and it is also used in construction and road construction (alternatives to aggregates).
Conclusion: The high capacity of Dolochar in waste absorption and wastewater treatment shows that it is necessary to reuse it in Iran instead of burying or leaving it in the environment.

Background and Objective: Wastewater produced in industrial estates is crucial to address due to the wide range of pollutants it contains. The objective of the present study was to investigate the performance of the Chamshahr Industrial Estate Wastewater Treatment Plant for effluent and sludge reuse.
Materials and Methods: In this descriptive and comparative study, the quality of raw industrial wastewater, effluent, and sludge from the wastewater treatment plant of the Chamshahr Industrial Estate was investigated over three periods at monthly intervals. Additionally, archival quality data for wastewater, effluent, and sludge from 1402 to 1403 were analyzed. The results were compared with the standards and guidelines of Iran, WHO, FAO, USEPA, and others. The wastewater treatment method employed a combination of chemical sedimentation and aerated lagoons with return sludge.
Results: The volume of wastewater produced in this industrial estate was 15,000 m³/day, primarily originating from leather and tanning industries (6,100 m³/day), which exhibit high pollution intensity. The treatment plant's efficiency in removing BOD, COD, and TSS was 62±24%, 72±19%, and 84±13%, respectively. However, due to the concentration of heavy metals, such as chromium in the wastewater (0.28 mg/L) and sludge (353.5 mg/L), the treatment method was unable to meet existing standards and guidelines. Furthermore, the salt content in the effluent (43,300 mg/L) and sludge (202,000 mg/L) was excessively high, rendering it unsuitable for disposal or reuse without further treatment.
Conclusion: The performance of the wastewater treatment plant fails to meet the standards and guidelines for environmental discharge and the reuse of effluent and sludge. Therefore, the final effluent and sludge require additional treatment to enable reuse and prevent environmental pollution.
 

Background and Objective: This study aimed to assess the chemical and microbial quality of sludge generated at the Khoy wastewater treatment plant using an SBR process, and to compare the results with established agricultural standards.
Materials and Methods: In this study, monthly sludge samples were collected and analyzed using standard EPA methods, including the 15-tube technique for coliforms, flotation for Ascaris eggs, and acid digestion for heavy metals. Data were analyzed using SPSS v.25 and statistical analyses included Pearson correlation tests.
Results: The analyzed sludge exhibited an acceptable pH (7.14) and a high organic carbon content (27.32%). However, its elevated salinity (9891 µS/m) and low C/N ratio (6.38) indicated biological instability and limitations for direct agricultural application. The concentrations of heavy metals—including arsenic (10.27 mg/kg), copper (134.86 mg/kg), and zinc (530.93 mg/kg)— exceeded Iran’s national standards. Heat-map analysis confirmed a significant correlation between salinity, and the levels of chloride (Cl^-), and sulfate (SO₄^2-). Despite its nutritional value, the sludge is not recommended for direct agricultural use without prior treatments such as stabilization, salinity reduction, and pathogen removal.
Conclusion: Despite the substantial nutrient content of the sludge, including nitrogen, phosphorus, and organic carbon, its direct application in agriculture faces serious limitations due to high salinity, an imbalanced C/N ratio, severe microbial contamination (e.g., nematode eggs), and the exceedance of permissible levels for several heavy metals. Safe utilization of this sludge requires corrective treatments such as stabilization, disinfection, desalination, and regular monitoring of heavy metal concentrations.