Isotherms, kinetics and thermodynamic mechanism of methylene blue dye adsorption on synthesized activated carbon.

The treatment of methylene blue (MB) dye wastewater through the adsorption process has been a subject of extensive research. However, a comprehensive understanding of the thermodynamic aspects of dye solution adsorption is lacking. Previous studies have primarily focused on enhancing the adsorption capacity of methylene blue dye. This study aimed to develop an environmentally friendly and cost-effective method for treating methylene blue dye wastewater and to gain insights into the thermodynamics and kinetics of the adsorption process for optimization. An adsorbent with selective methylene blue dye adsorption capabilities was synthesized using rice straw as the precursor. Experimental studies were conducted to investigate the adsorption isotherms and models under various process conditions, aiming to bridge gaps in previous research and enhance the understanding of adsorption mechanisms. Several adsorption isotherm models, including Langmuir, Temkin, Freundlich, and Langmuir-Freundlich, were applied to theoretically describe the adsorption mechanism. Equilibrium thermodynamic results demonstrated that the calculated equilibrium adsorption capacity (qe) aligned well with the experimentally obtained data. These findings of the study provide valuable insights into the thermodynamics and kinetics of methylene blue dye adsorption, with potential applications beyond this specific dye type. The utilization of rice straw as an adsorbent material presents a novel and cost-effective approach for MB dye removal from wastewater.

Evaluation of the surface water quality using global water quality index (WQI) models: perspective of river water pollution.

Rapid industrialization, urbanization, global warming, and climate change are compromising surface water quality across the globe. Consequently, water conservation is essential for both environmental sustainability and human survival. This study assesses the water quality of the Jamuna River in Bangladesh at five distinct sites during wet and dry seasons. It employs six global water quality indices (WQIs) and contrasts the results with Bangladesh's Environmental Quality Standard (EQS) and the Department of Environment (DoE) criteria. The WQI models used are the Weighted Arithmetic WQI (WAWQI), British Columbia WQI (BCWQI), Canadian Council of Ministers of the Environment WQI (CWQI), Assigned WQI (AWQI), Malaysian WQI (MWQI), and Oregon WQI (OWQI). Fifteen physicochemical parameters were analyzed according to each WQI model's guidelines. The findings reveal that most parameters surpass the standard permissible values. The WQI model results indicate that the average water quality across the five sites falls into the lowest category. A comparison of the WQI models suggests potential correlations between WAWQI and AWQI, as well as between MWQI and OWQI. The straightforward presentation of the WQI models indicates that while the river water requires treatment for household and drinking use, it remains suitable for irrigation. The decline in water quality is likely attributable to human activities, urbanization, municipal waste disposal, and industrial effluents. Authorities must prioritize regular monitoring and assessment of water quality to address the identified challenges. Restoring the water to an acceptable standard will become increasingly difficult without proactive measures.

The effect of climate change on domestic Rainwater Harvesting.

One of the main strategies that are being applied to improve the efficiency of water consumption in buildings is the use of non-potable water for pavement washing, toilet flushing, irrigation, and others. According to several guidelines, the design and assessment of a Rainwater Harvesting System (RWHS) should be made using recent official records of precipitation. However, there is not an indication whether historical or future projections should be used, leaving space for the designer to choose. This article presents the study of RWHS in southern Europe, namely in Portugal, considering two case studies (a dwelling in Oporto and an apartment in Vila Real). The main goal was to explore the impacts that climate change will have on these systems and, for that purpose, a daily simulation using future rainfall data was performed for both cases considering two scenarios: RCP 4.5 which is more optimistic, and RCP 8.5 which is more pessimistic. The RWHS in Oporto showed a better performance in the future decades, comparing with simulations based on recent decades, for both scenarios. However, the savings will not have a significant variation (less than 5 €/year). In the future, this system will provide around 47 (±2.4) m3 of rainwater per year to the selected non-potable purposes, leading to savings of around 66 (±3.3) €/year. Vila Real case study also revealed a slight improvement of the system's efficiency in the future decades but the results for rainwater collected and used are so similar to the recent ones that it can be concluded that the performance will be sustained. This system will provide around 50 (±2.5) m3 of rainwater per year to the selected non-potable purposes, leading to savings of around 200 (±10.2) €/year. It can be concluded that there will be no significant changes in RWHS performance in the future, in the studied areas.

Optimise inlet condition and design parameters of a new sewer overflow screening device using numerical model.

After heavy rainfall, sewer overflow spills to receiving water bodies cause serious concern for the environment, aesthetics and public health. To overcome these problems this study investigated a new self-cleansing sewer overflow screening device. The device has a sewer overflow chamber, a rectangular tank and a slotted ogee weir to capture the gross pollutants. To design an efficient screening device a numerical computational fluid dynamic (CFD) model was used. A plausibility check of the CFD model was done using a one-dimensional analytical model. Results showed that an inlet parallel to the weir ensured better self-cleansing than an inlet perpendicular to the weir. Perforations should be at the bottom of the weir to get increased velocity and shear stress to create a favourable self-cleaning effect of the screening device. Increasing inlet length from 0.3 to 1.5 m reduced wave reflection up to 10%, which increased flow uniformity downstream and improved self-cleansing effect. The orientation of the ogee weir with the rectangular tank was found most uniform with a 1:3 (horizontal:vertical) slope. These results will help to maximise functional efficiency of the new sewer overflow screening device. Otherwise it would be too expensive to alter after installation and at times difficult to customise accordingly to existing urban drainage systems.

Role of NGOs and CBOs in Waste Management.

BACKGROUND: Developing cities like Khulna, the third largest metropolitan city in Bangladesh, have now begun to confess the environmental and public health risks associated with uncontrolled dumping of solid wastes mainly due to the active participation of non-governmental organizations (NGOs) and community-based organizations (CBOs) in municipal solid waste (MSW) management. METHODS: A survey was conducted to observe the present scenarios of secondary disposal site (SDS), ultimate disposal site (UDS), composting plants, medical wastes management and NGOs and CBOs MSW management activities. RESULTS: A total of 22 NGOs and CBOs are involved in MSW management in 31 wards of Khulna City Corporation. About 9 to 12% of total generated wastes are collected by door-to-door collection system provided by mainly NGOs and CBOs using 71 non-motorized rickshaw vans. A major portion of collected wastes is disposed to the nearest SDS by these organizations and then transferred to UDS or to private low-lying lands from there by the city authority. A small portion of organic wastes is going to the composting plants of NGOs. CONCLUSION: The participation of NGOs and CBOs has improved the overall MSW management system, especially waste collection process from sources and able to motivate the residents to store the waste properly and to keep clean the premises.

Select chemical and engineering properties of wastewater biosolids.

The select chemical and engineering characteristics of biosolids produced at a wastewater treatment plant in Eastern Australia were investigated to assess its suitability as structural fill material in road embankments. Results of comprehensive set of geotechnical experimentation including compaction, consolidation, creep, hydraulic conductivity and shear strength tests implied that biosolids demonstrate behavior similar to highly organic clays with a higher potential for consolidation and settlement. Results of chemical study including heavy metals, dichloro diphenyl trichloroethane (and derivatives) and organochlorine pesticides, indicate that biosolids samples are within the acceptable limits which allows their usage under certain guidelines. Results of tests on pathogens (bacteria, viruses or parasites) also indicated that biosolids were within the safe acceptable limits. Technical and management suggestions have been provided to minimize the possible environmental risks of using biosolids in road embankment fills.

First-order hydrothermal oxidation kinetics of digested sludge compared with raw sludge.

This article presents an assessment of the first-order hydrothermal oxidation kinetics of a selected digested sludge at subcritical (< 374 degrees C) and supercritical (> 374 degrees C) temperatures in the range of 250-460 degrees C. Furthermore, the results were compared with reported oxidation kinetics of raw sludge treated under identical experimental conditions. In the assessment, oxidation was considered to proceed in two steps: (1) decomposition of the particulate, or non-filterable, chemical oxygen demand (PCOD); followed by (2) ultimate oxidation and removal of the total, particulate and soluble, COD. The accumulation and removal of soluble COD (SCOD) was determined from the difference between the rates of sludge decomposition and ultimate oxidation. Using results from batch and continuous-flow hydrothermal treatment experiments, the reacting organic ingredients were separated into groups according to the ease or difficulty at which they were decomposed or removed, with Arrhenius-type activation energy levels assigned to the different groups. The analysis confirmed that within the treatment range of 75% to more than 97% COD removal, the oxidation kinetics of the digested and raw sludges were nearly identical despite differences in the proportions of their original organic ingredients. The original organic ingredients were mostly removed above 75% COD removal, and the oxidation kinetics appeared to be dominated by the removal of acetic acid, an intermediate by-product which constituted 50% to more than 80% of the remaining COD. Furthermore, the oxidation kinetics of both sludge types were consistent with reported first-order oxidation kinetics of pure acetic acid solutions. The resulting kinetic models adequately represented hydrothermal oxidation of digested sludge, in terms of COD and PCOD removals, as well as accumulation and removal of the soluble SCOD.