Response Surface Modelling of Methylene Blue Adsorption onto Seaweed, Coconut Shell and Oak Wood Hydrochars

Adsorption of methylene blue (MB) dye from an aqueous solution onto hydrochars produced from brown seaweed (Fucus Serratus) (FS-HC), coconut shell (CS-HC), and oak wood (Oak-HC) at different temperatures (200–250 °C) was investigated in a batch system. Response surface modelling (RSM) was used to investigate the effect of initial MB concentration (50–300 mg/L), contact time (0–240 min), and solution pH (2–12) on the adsorption process. RSM was also used to model and optimise these parameters for efficient adsorption. Kinetic and isotherms studies were carried out to study the adsorption mechanism onto the hydrochars. It was found that the best adsorbent from the RSM model was FS-HC200, and the optimal conditions for greater MB dye uptake were lower initial MB concentration (50 mg/L), pH 6 and contact time of 84 min; removing >99% of MB. Langmuir and Redlich–Peterson isotherm models fitted the adsorption of MB onto hydrochars prepared at 200 and 250 °C. Freundlich and Redlich–Peterson isotherms were suitable for hydrochars produced at 220 °C. FS-HCs have the highest maximum adsorption capacity of MB of about (8.60–28.57) mg/g calculated from the Langmuir isotherm. The adsorption process for all the hydrochars followed a pseudo-second-order model (R² = 0.96–1.00), and film diffusion and intraparticle diffusion were the rate-determining steps. Therefore, this work identifies cheap adsorbents from biowaste that are effective for the removal of cationic pollutants from wastewater

A toilet system based on hydrothermal carbonization

We are developing a toilet system that converts faecal material to an aqueous suspension of carbonised material that is safe to handle, and readily separated from the remaining liquid. It will also extract useful salts from the liquid. The system is aim to be the new generation universally appealing toilet and it will be of particular and urgent interest to areas where no (or very crude) sanitation exists. The system is designed to be self-sufficient in terms of energy input and to scale for a number of users in the range a few tens to a thousand or more. In parallel with our engineering development we are designing the system to provide users with a positive and comfortable experience. Hydrothermal carbonisation (HTC) has received attention recently as a way to convert biomass - including sewerage - into coal like material. It involves heating the start material in water at high temperatures and pressures. Depending on the conditions used the process can produce hydrocarbon gases or liquids or coal like particles. Most HTC work involving sewerage treatment is currently aimed at replacing established large-scale treatment plants i.e. for places with well-developed sewerage services. Our system, using HTC, is aimed at bringing the process at a decentralized household ( including combination of households) level so that the new generation toilet become accessible to all and particularly to those areas where none currently exists. Using HTC for toilets on continuous basis for such a small scale is the key innovation of our proposed system. We will describe our work to characterise the energetics of the HTC process in order to optimise the process in terms of total energy input and how we have used this information to develop a continuous system based on a plug flow reactor. The material produced by the system can be easily separated from the remaining liquid and used to generate heat and power (via a generator including solar) in order to maintain the process. The solids are safe to handle, and look, feel and smell much like coffee grounds. In situations where electrical (or renewable energy like solar) power is available the solid material can be used either as a fuel for heating and cooking, as a soil conditioner and possibly for carbon capture. We will discuss the possibility of including other waste material (food, sanitary waste etc.) into the system. In order to minimize the amount of water required to flush material away from the toilet bowl and to help maintain high sanitary standards we have been investigating anti-fouling coatings for the system. We will describe the results of studies of a nano-coating based on a responsive polymer that significantly enhances the rate at which water flushes away material that adheres to the toilet surface

Cross-Location Analysis of the Impact of Household Socioeconomic Status on Participation in Urban and Peri-Urban Agriculture in West Africa

This study explores the relation between household socioeconomic status (SES) and participation in urban and periurban agriculture (UPA) in three West African cities. We used a structured questionnaire to survey 700 randomly selected households: 250 in Kano, Nigeria, 250 in Bobo Dioulasso, Burkina Faso, and 200 in Sikasso, Mali. Multiple correspondence analysis was applied on household asset variables to create an index of assets which was used as a proxy for household SES. The results showed no significant differences in households’ rate of participation in UPA across socioeconomic groups. Participation in UPA was rather significantly (P < 0.001) and positively related to household size. Interestingly, the analysis revealed that field crop cultivation and gardening were more common among households in the low and medium SES groups while those in the high SES group were more likely to keep livestock

Hydrochars Produced by Hydrothermal Carbonisation of Seaweed, Coconut Shell and Oak: Effect of Processing Temperature on Physicochemical Adsorbent Characteristics

The present study addresses the production of hydrochars from brown seaweed (Fucus Serratus) (FS-HCs), coconut shell (CS-HCs), and oak (Oak-HCs) as potential adsorbents using hydrothermal carbonisation (HTC). The effect of HTC processing temperature on the physicochemical adsorbent characteristics of the hydrochars is investigated at different temperatures (200, 220, 250 ºC) using a hydrothermal batch reactor. Increasing HTC temperature causes the formation of many spheres in CS-HCs and Oak-HCs, increasing their porosity, except FS-HCs. The surface area of the hydrochars increases with increasing HTC temperature; 10.93–12.78 m²/g for FS-HCs, 2.18–21.94 m²/g for CS-HCs, except for Oak-HCs which decreases from 4.89–3.09 m²/g. Increasing HTC temperature decreases volatile matter content in the hydrochars, increases fixed carbon content, and decreases H/C ratio (except for FS-HCs) and O/C ratio of the hydrochars. For all the hydrochars, increasing the HTC temperature results in a slight decrease in zeta potential magnitude, with negatively charged surfaces, making them potential adsorbents for cationic pollutants. The study confirms that the HTC process improves key chemical and physical characteristics of the hydrochars compared to the original biomass, and that the physicochemical adsorbent characteristics are enhanced as the processing temperature increases

Production and characterisation of adsorbents synthesised by hydrothermal carbonisation of biomass wastes

Surface structure and chemical properties of adsorbents are important factors required to understand the mechanism of adsorption. The purpose of this study was to produce hydrochars from biomass using hydrothermal carbonisation (HTC) and to analyse their sorption capacities. The biomass used in this study were coco-peat (CP), coconut shell (CS), eggshell (ES), rice husk (RH) and lemon peel (LP). The operating conditions for HTC were 200 °C and 20 h residence time. The characterisation methods consisted of Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), Fourier Transform Infrared Ray (FTIR) Spectroscopy, and Brunauer, Emmett and Teller (BET). The results showed that HTC improved the sorption capacities of the biomass wastes. It was found that hydrochars were crispy and flaky with more micro- and meso-porous structures, indicating that lignin and other components were denatured due to carbonisation. This led to the creation of more active sites for sorption and pollutant binding. The hydrochars showed a percentage increase in carbon content and a decrease in oxygen content with traces of other elements, compared to their corresponding raw biomass. The major functional groups identified were –OH and –COOH. The surface area of the hydrochars which include CP (2.14 m2/g), CS (14.04 m2/g), ES (0.50 m2/g), RH (15.74 m2/g), and LP (6.89 m2/g) were significantly improved compared with those of the raw biomass. The study showed that the hydrochars produced from the biomass wastes have the potential to be used as adsorbents

Resilient Lagoons? Climate change, sustainability and adaptation

Lagoons are found at low-lying coastlines around the globe (Figure 1) and their associated wetlands are important dynamic environments. Ensuring the sustainability of the world’s lagoons is vital for communities, ecosystems and economies. Lagoons support highly productive ecosystems and provide critical ecosystem services, societal benefits and myriad fundamental and valuable resources that are vital for the wellbeing and livelihoods of coastal communities. Yet, the sustainability of lagoons and the communities who rely on them are under increasing pressure from a complex set of interconnected issues, including climate change, sea-level rise, pollution, poor waste management, population growth and policy approaches that favour top-down governance to the exclusion of local knowledges and priorities (Convention on Wetlands, 2021). This article summarises the latest research on lagoons using the examples of Muni Lagoon in Ghana and Lagos Lagoon in Nigeria (Figure 1). It also draws from the interdisciplinary dialogues emerging through the Global Challenges Research Fund (GCRF)-funded Resilient Lagoon Network (see website), which seeks to challenge top-down management approaches and instead prioritise participatory approaches that value local knowledges and in which coastal communities are central to resilient lagoon governanc