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This study presents a systematic study on sequential treatment of highly resistant landfill leachate by electrocoagulation (EC)/aeration, sulfate radical advanced oxidation process (SR-AOP) and electro-Fenton (EF). In case of SR-AOP, peroxymonosulfate (PMS) catalyzed by zero valent iron (ZVI) and ultraviolet irradiation (UV) system was developed. Treatment process was optimized in respect to COD removal. Analysis of results revealed that sequential application of EC/aeration, PMS/ZVI/UV, and EF processes provide an extraordinary performance and meet the environmental regulations. The source of iron for EF process was provided from previous process reducing the cost of sequential process. Separately, EC/aeration (inlet COD = 4040 mg/L), PMS/ZVI/UV (inlet COD = 1560 mg/L), and EF (inlet COD = 471 mg/L) removed 61, 69 and 82% of COD respectively. Overall, sequential processes of EC/aeration, PMS/ZVI/UV and EF could remove the COD, TOC and ammonia of the landfill leachate around 98%, 93% and 94%, respectively. The comparison of different sequences of following processes indicated that current configuration (EC/aeration-PMS/ZVI/UV-EF) could meet the discharge standards. Furthermore, humification degree was significantly improved after oxidative processes. Biodegradability study was also performed by means of BOD/COD, average oxidation state (AOS), and Zahn-Wellens test, and the best results associated with these indices were obtained 0.56, 2.37, and over 98%, respectively. Phytotoxicity of leachate was remarkably reduced and the final effluent can be considered as a non-phytotoxic wastewater.

Chemical pollution in the Persian Gulf has become an important health concern in recent decades. This investigation aimed to meta-analyses of potential toxic elements (PTEs) including lead (Pb), inorganic Arsenic (As), Cadmium (Cd), Nickel (Ni) and Mercury (Hg) in the coastal sediment of the Persian Gulf. In this study, an attempt was made to retrieve papers conducted on the concentration of PTEs in the coastal sediment of the Persian Gulf by searching in international databases including Web of Science, Scopus, Embase and PubMed. Meta-analysis concentration of PTEs in the coastal sediment of the Persian Gulf was conducted using random effects model based on the country subgroup. Additionally, non-dietary risk assessment including non-carcinogenic and carcinogenic risks from ingestion, inhalation and dermal contact routes and ecological risk assessment was estimated. Seventy-eight papers with 81 data-reports (1650 sample size) were included in our meta-analysis. The rank order of heavy metals in coastal sediment of the Persian Gulf based on pooled concentration was Ni (65.44 mg/kg) > Pb (58.35 mg/kg) > As (23.78 mg/kg) > Cd (1.75 mg/kg) > Hg (0.77 mg/kg). The highest concentration of As, Cd, Pb, Ni and Hg was observed in the coastal sediment of Saudi Arabia, Arab Emirates, Qatar, Iran and Saudi Arabia, respectively. Although the Igeo index in coastal sediment of the Persian gulf was in Grade 1 (Uncontaminated) and grade 2 (slightly contaminated) but total target hazard quotient (TTHQ) of adults due to As and Cd and Adolescent due to As, Cd, Pb and Niwas higher than 1 value In Iran, In Saudi Arabic, TTHQ of adults due to As and Cd and adolescent due to As and Cd was higher than 1 value, In United Arab Emirates, TTHQ of adults due to Cd and Adolescents due to As, Cd and Pb were higher than 1 value and In Qatar, TTHQ of adults age group due to Pb and adolescent age group due to Pb was higher than 1 value. Total cancer risk (TCR) for adults and adolescent due to As was higher than 1E-6 in Iran, United Arab Emirates and Qatar but TCR for adolescents due to As was higher than 1E-6 in Saudi Arabic. Therefore, it is recommended to monitor the concentration of PTEs and implementation of programs to reduce the emission of PTEs from resources in the Persian Gulf.