Effect of coagulation and sonication on the dissolved air flotation (DAF) process for thickening of biological sludge in wastewater treatment

Background: Dissolved air floatation (DAF) is one of the methods has been used for the sludge thickening in wastewater treatment plants. This study aimed to investigate the effects of coagulation and sonication processes as additional configurations on the efficiency of a lab-scale DAF process for thickening of the biological sludge of an industrial wastewater treatment plant in Kashan, Iran. Methods: The required amounts of sludge samples were collected from a wastewater treatment plant and kept at temperature of 4°C. Variables, such as pressure (3, 5, and 7 atm), flotation time (5 and 10 minutes), ultrasonic irradiation power (0, 75, and 150 W), and presence/absence of Fe-based coagulant were considered on a sequencing batch reactor (SBR) included coagulation, flotation, and sonication processes, respectively. Results: The use of ultrasonic waves led to an insignificant increase in the DAF efficiency (P > 0.05), however, the application of coagulant significantly increased the thickening efficiency (P < 0.05). The maximum efficiency of the process was achieved at flotation time of 5 min, pressure of 3 atm, and sonication power of 75 W. Conclusion: According to the results, DAF has a proper efficiency for thickening of biological sludge. Coagulation compared to sonication has a greater effect on the efficiency of the process. Keywords: Ultrasonic waves, Industrial effluent, Dissolved air flotation, Sonicatio

Critical air pollutant assessments and health effects attributed to PM2.5 during and after COVID-19 lockdowns in Iran: application of AirQ+ models

ObjectivesThe aim of this study was to evaluate changes in air quality index (AQI) values before, during, and after lockdown, as well as to evaluate the number of hospitalizations due to respiratory and cardiovascular diseases attributed to atmospheric PM2.5 pollution in Semnan, Iran in the period from 2019 to 2021 during the COVID-19 pandemic.MethodsDaily air quality records were obtained from the global air quality index project and the US Environmental Protection Administration (EPA). In this research, the AirQ+ model was used to quantify health consequences attributed to particulate matter with an aerodynamic diameter of &lt;2.5 μm (PM2.5).ResultsThe results of this study showed positive correlations between air pollution levels and reductions in pollutant levels during and after the lockdown. PM2.5 was the critical pollutant for most days of the year, as its AQI was the highest among the four investigated pollutants on most days. Mortality rates from chronic obstructive pulmonary disease (COPD) attributed to PM2.5 in 2019–2021 were 25.18% in 2019, 22.55% in 2020, and 22.12% in 2021. Mortality rates and hospital admissions due to cardiovascular and respiratory diseases decreased during the lockdown. The results showed a significant decrease in the percentage of days with unhealthy air quality in short-term lockdowns in Semnan, Iran with moderate air pollution. Natural mortality (due to all-natural causes) and other mortalities related to COPD, ischemic heart disease (IHD), lung cancer (LC), and stroke attributed to PM2.5 in 2019–2021 decreased.ConclusionOur results support the general finding that anthropogenic activities cause significant health threats, which were paradoxically revealed during a global health crisis/challenge

Bioremediation of the Soils Contaminated with Cadmium and Chromium, by the Earthworm Eisenia fetida

One of the most important environmental problems in the world is the soils contamination by heavy metals in the industrial areas, and especially the contamination of the agricultural lands. The use of earthworms to bioremediate the soils results in reducing the pollutants concentration through a bioaccumulation mechanism on the contaminants in the earthworm's body. Hence, the present study aimed to prove the biological effectiveness of Eisenia fetida earthworms in bioremediation the soils contaminated with chromium and cadmium. Concentration of chromium and cadmium pollution in soil was determined to be 0.04 mg/g and 0.08 mg/g respectively. 30 worms were added to 500 g soil samples. Chromium and cadmium concentration in soil and in the body of worms was measured at two time periods of 21 and 42 days. To measure the concentration of chromium and cadmium we used ICP spectrometry. Software in usage was SPSS version 17. There was a significant correlation between the reduction of chromium and cadmium metals in the soils and the accumulation of chromium and cadmium metals in the worm’s body. A significant decline of chromium levels of the soil was observed in the days 21 and 42 during the study compared to initial amount of 0.1 mg/g. on the other hand chromium concentration of the soil decreased from 0.14 mg/g to 0.1 mg/g after 42 days. Comparison of mortality in two different time periods showed that by passing the time and by increase in soil chromium and cadmium concentrations the death toll of worms rises. The increased mortality of worms in the soil at a concentration of 0.08 mg/g of chromium, say that using the worms for bioremediation is not recommended at such concentration of chromium but using the worms for the removal of cadmium at concentrations of 0.04 mg/g and 0.08 mg/g in the soil is recommended

Study of electrochemical process effect on detergent removal from polluted water and fish bioassay test of the effluent

Aims: Linear alkylbenzene sulfonate (LAS) is an anionic surfactant which is widely used in household and industrial detergents usage, and after use, it usually finds a way to the wastewater treatment systems. Conventional treatment is not recognized as an efficient method due to the long residence time and enlarged cost. Hence, advanced oxidation processes including electrochemical techniques are important. In this paper, electrochemical degradation of a synthetic solution of LAS with initial concentration 200 ppm has been investigated. Methods: The experiment was performed using eight stainless steel electrodes as cathode and anode with a monopolar arrangement. The effects of current intensity and density were studied as operational parameters on detergent removal efficiency. Results: The maximum removal efficiency 94% was achieved at current intensity equal to 300 mA and current density 6 mA/cm2. The energy consumption was calculated 2.7 ± 0.1 WH/g. The bioassay test showed that only under optimum conditions, 80% of fish was survived until 4 days since the end of the process and the rest were died immediately. All ten fish leaved in unpolluted were survived until 4 days monitoring. Conclusion: The results showed that, by reducing the current density, removal efficiency increases it was true for all current intensities

Long-term trends of Nitrogen oxides and surface ozone concentrations in Tehran city, 2002–2011

Background and aim: Tropospheric ozone is a problem with multi aspects - hazard to human health, plant, and welfare and a key factor to climate change, air pollution and atmosphere chemistry, as well. Behavior of ozone and nitrogen oxides (NO, and NO<inf>2</inf>) concentration is highly complex and variable; therefore, their trends as short and long-term were significantly attended. Most of the studies were carried out on the behavior of pollutant concentrations in North America, Europe, and East Asia, but few studies have been conducted in west Asia. The aim of this study was to assess daily changes and long-term trend of ozone and nitrogen oxides concentrations in Tehran city, Iran from March 2002 to September 2011. Material and methods: Data were collected from 18 air quality monitoring stations. The data were sorted as daily mean of 10 years (daily changes) and annual mean for each year (long-term trend). One-sample test was used to assess the statistical significance. Results: Current findings indicated that changes of ozone, NO, and NO<inf>2</inf> concentrations are dependent from job shifts and photochemical reactions. Annual mean concentrations of ozone and NO<inf>2</inf> were gradually increased, long-term trend of ozone and NO<inf>2</inf> concentration indicated. The correlation between long term trend of ozone and NO<inf>2</inf> was significant (p < 0.05). Conclusion: The controlling program was the most important factor in long-term concentration of ozone, and nitrogen oxides, but some problems and difficulties were accounted to perform controlling program. © 2015 Motesaddi Zarandi et al

Long-term trends of Nitrogen oxides and surface ozone concentrations in Tehran city, 2002–2011

Background and aim: Tropospheric ozone is a problem with multi aspects - hazard to human health, plant, and welfare and a key factor to climate change, air pollution and atmosphere chemistry, as well. Behavior of ozone and nitrogen oxides (NO, and NO2) concentration is highly complex and variable; therefore, their trends as short and long-term were significantly attended. Most of the studies were carried out on the behavior of pollutant concentrations in North America, Europe, and East Asia, but few studies have been conducted in west Asia. The aim of this study was to assess daily changes and long-term trend of ozone and nitrogen oxides concentrations in Tehran city, Iran from March 2002 to September 2011. Material and methods: Data were collected from 18 air quality monitoring stations. The data were sorted as daily mean of 10 years (daily changes) and annual mean for each year (long-term trend). One-sample test was used to assess the statistical significance. Results: Current findings indicated that changes of ozone, NO, and NO2 concentrations are dependent from job shifts and photochemical reactions. Annual mean concentrations of ozone and NO2 were gradually increased, long-term trend of ozone and NO2 concentration indicated. The correlation between long term trend of ozone and NO2 was significant (p < 0.05). Conclusion: The controlling program was the most important factor in long-term concentration of ozone, and nitrogen oxides, but some problems and difficulties were accounted to perform controlling program. © 2015 Motesaddi Zarandi et al