Microbial Desalination Cell for Sustainable Water Treatment: A Critical Review.

In view of increasing threats arising from the shortage of fresh water, there is an urgent need to propose sustainable technologies for the exploitation of unconventional water sources. As a derivative of microbial fuel cells (MFCs), microbial desalination cell (MDC) has the potential of desalinating saline/brackish water while simultaneously generating electricity, as well as treating wastewater. Therefore, it is worth investigating its practicability as a potential sustainable desalination technology. This review article first introduces the fundamentals and annual trends of MDCs. The desalination of diverse types of solutions using MDCs along with their life cycle impact assessment (LCIA)  and economic analysis is studied later. Finally, limitations and areas for improvement, prospects, and potential applications of this technology are discussed. Due to the great advantages of MDCs, improving their design, building materials, efficiency, and throughput will offer them as a significant alternative to the current desalination technologies.

The impact of irrigation with treated wastewaters on soil and kikuyu grass nutrient compositions.

A lysimeter study was conducted for 1 year to examine how the source of wastewater for irrigation impacted soil physicochemical properties and kikuyu grass (Pennisetum clandestinum) nutrient composition. The wastewater used included treated wastewater produced by a membrane bioreactor (MBR) and intermittently decanted aerated lagoon (IDAL) treatment systems. No significant differences were observed between the treatments regarding total nitrogen and total phosphorus across the depths of the columns. However, highly significant differences were observed for Na content of the soils at various depths. Remarkable differences were recorded for soil exchangeable K and Na at different depths. In contrast, soil exchangeable Ca and Mg experienced no significant differences concerning the depth of the columns. For kikuyu grass, sodium contents of the grasses irrigated with MBR and IDAL treated wastewaters increased more than 200% and 100%, respectively, when compared with the grass irrigated with tap water. Over the period of monitoring considered in this study, there was no sign of excessive soil salinity/sodicity issues. The MBR treated wastewater has the potential to supply the grass with a constant dosage of valuable nutrients such as N and P without the requirement of using chemical fertilizers. This reduces the risk of contamination of receiving waters and groundwater and enhances the recycling of the nutrients in the wastewater to achieve a circular economy of nutrients. PRACTITIONER POINTS: Application of treated wastewaters revealed no harmful effects on soil and plant nutritional properties over the study period. The membrane bioreactor (MBR) treated wastewater potentially supplies the grass with constant dosage of valuable nutrients in the absence of chemical fertilisers. Sodium contents of the grasses irrigated with MBR and IDAL treated wastewaters increased more than 200% and 100%, respectively. Soil soluble and exchangeable cations showed very similar trends of changes versus the depth of the soil over the study period.

A Food Waste-Derived Organic Liquid Fertiliser for Sustainable Hydroponic Cultivation of Lettuce, Cucumber and Cherry Tomato.

We previously reported a sustainable food waste management approach to produce an acceptable organic liquid fertiliser for recycling food waste called "FoodLift." This study follows our previous work to evaluate the macronutrients and cation concentrations in harvested structural parts of lettuce, cucumber, and cherry tomatoes produced using food waste-derived liquid fertiliser (FoodLift) and compare them against commercial liquid fertiliser (CLF) under hydroponic conditions. N and P concentrations in the structural parts of lettuce and the fruit and plant structural parts of cucumber appear to be similar between FoodLift and CLF (p > 0.05), with significantly different N concentrations in the various parts of cherry tomato plants (p < 0.05). For lettuce, N and P content varied from 50 to 260 g/kg and 11 to 88 g/kg, respectively. For cucumber and cherry tomato plants, N and P concentrations ranged from 1 to 36 g/kg and 4 to 33 g/kg, respectively. FoodLift was not effective as a nutrient source for growing cherry tomatoes. Moreover, the cation (K, Ca, and Mg) concentrations appear to significantly differ between FoodLift and CLF grown plants (p < 0.05). For example, for cucumber, Ca content varied from 2 to 18 g/kg for FoodLift grown plants while Ca in CLF-grown cucumber plants ranged from 2 to 28 g/kg. Overall, as suggested in our previous work, FoodLift has the potential to replace CLF in hydroponic systems for lettuce and cucumber. This will lead to sustainable food production, recycling of food waste to produce liquid fertiliser, and will promote a circular economy in nutrient management.

Microplastics in urban stormwater-developing a methodology for its monitoring.

This study presents microplastics results for stormwater collected in retention ponds. A novel procedure was developed to collect microplastic (MP) particles by filtering stormwater using a purpose-built cascade filtration setup which included 4 steel filters of pore size, 48.5, 170, 2500 and 5000 µm. Based on the methodologies proposed in the literature, a novel procedure was developed incorporating a combination of optical and FTIR methods for quantification and identification of microplastics. The developed methodology was applied for determining and characterising MP from two retention ponds. Average concentrations of 2067 and 2133 MP/m3 were observed, respectively, for dry and wet periods at site 1. Similar concentrations were observed for site 2. The results showed a slight increase in the microplastics concentration for the wet period. Most MP particles existed in the size range 48.5-170 µm and 170-2500 µm. Among the type of MP particles, polyester was significantly more abundant than other types of plastics (78-94%). Comparing the data obtained in this study with those from the literature, it was apparent that the stormwater originated from two urban catchments has been subjected to considerable microplastic contamination. This can be attributed to anthropogenic activities in urban areas. Microplastic particles in the stormwater can have an adverse impact on aquatic life present in the receiving water bodies. Also, the presence of MP may suggest the existence of nanoplastics in urban stormwater. This finding can have broader implications for urban stormwater management.

Recycling of food waste to produce chicken feed and liquid fertiliser.

Most of the food waste (FW) generated by commercial activities and the majority of household FW is collected as part of general waste, which is either incinerated or landfilled. There is an increasing interest in the collection of FW as a separate waste stream and use it for the production of compost or recovery of energy through anaerobic digestion (AD) or pyrolysis. This study focused on using FW to produce chicken feed and liquid fertiliser (CFLF). The food waste samples were collected from food related businesses such as service club, café, restaurant, bakery and supermarket. The CFLF process was used to produce chicken feed pellets containing 19% of protein content, which is within the range of 16 to 22% of most commercial chicken feed pellets and within the National Research Council (NRC) recommended range of 15 to 23%. The liquid extract derived from CFLF process had high nutrient concentrations similar to those present in the feed solution used in hydroponic systems. Hence, the liquid extract from CFLF can be used to replace the commercial liquid fertiliser used in hydroponic systems. Environmental impact analysis of CFLF process using GaBi life cycle analysis (LCA) software indicated that the CFLF process can yield environmental credits for 15 out of 19 categories of impacts considered in the analysis. The measured environmental credits were significantly higher than the other disposal options such as, anaerobic digestion (AD), incineration and landfill.

Transport and biotransformation of organic carbon and nitrate compounds in unsaturated soil conditions.

The lack of drinking water was one of the hot environmental issues that focused on the contaminants released from the failure of sanitary systems. Organic carbon and nitrate compounds were concerned since they represented a potential risk to human health and environment. Mathematical modelling was an effective tool for understanding and estimating the fate and transport of contaminants. An organic carbon and nitrate compounds transport model was developed using the mass balance concept. Richards and multiplicative Monod equations supported the estimating of advection-dispersion transport and biodegradation processes, respectively. The numerical solutions were obtained using the MATLAB programme. The model capability was evaluated using pilot scale experimental data. The depth-averaged time series of pressure head and contaminants concentration profiles were measured several times a week during 91 days. Simulations were found to provide reasonable agreement with the observed data. The aerobic biodegradation zone was observed within 15 cm depth of soil column. Even though the column was operated for 91 days, soil microbes were enough to retard these contaminants. This confirmed that the developed model could be applied to simulate the transport of the contaminants under real time boundary conditions.