As global consumption of finite raw materials continues to rise, so too does the amount of waste produced. In Europe for example, each citizen consumes an average of 15 tonnes of raw materials and produces on average 5 tonnes of waste every year. This places huge pressure on the environment, with increasing pollution of air, water and soil, and contributes significantly to climate change. In order to reduce the twin problems of consumption and waste production, the circular economy promotes reuse of so called ‘waste products’ to extend their life cycle for as long as possible. Very often however, it can be difficult to find a suitable use for these waste products without causing additional damage to the environment.

In this study we collected waste alum sludge residuals from a water treatment plant, and waste bauxite residue, commonly referred to as ‘red mud’ from an Aluminum processing plant. We then simulated their use, firstly in filter drains to capture excess Phosphorus in the drain flows (recycle 1), and then, once saturated with Phosphorus, applied them to a range of agricultural soils (recycle 2) to act as a slow release fertiliser. While Phosphorus is a key plant nutrient in soils, excessive amounts can leach through or along the soil, or be transported in surface runoff to streams and rivers after rainfall events. Such Phosphorus laden flows are a main cause of pollution to rivers and streams globally – this is termed eutrophication. The purpose of our study was to assess whether or not application of these residuals as fertiliser would increase the pollution risk of phosphorus from different soil types with a range of initial phosphorus concentrations over a 6-month period when subjected to repeated and onerous rainfall conditions.

Fig. 1. Schematic overview of study.

我们的研究发现,当剩余材料were mixed with the soils, the waste alum sludge from the water treatment plant was more successful than the red mud residuals at reducing pollutant flows from a wide range of phosphorus enriched soils. Then when we applied the Phosphorus enriched waste alum sludge and red mud residuals to the surfaces of grassed soils, we found that the polluting phosphorus loads did not increase above those of the natural occurring soils under repeated rainfalls. These were important findings because they meant that the waste products displayed an ability to bind in the available Phosphorus and release it slowly into the soil, at a rate more suited to plant uptake requirements. The key phosphorus binding mechanisms in the red mud residuals were its high calcium deposits, which attracted phosphorus ions, while the relatively high aluminium deposits in the water treatment residuals explained its ability to bind in the available phosphorus. The potential therefore of both products to act as a slow release fertiliser is promising. We then examined metal uptake concentrations in the plants over the study period to evaluate if these were affected by application of the residuals, which contained a variety of trace metals. Encouragingly, we found that there were only negligible differences in metal concentrations between plants taken from the soils which had received the residuals and those which had not; with the water treatment residuals impacting the least and therefore performing better. Our overall conclusion was that water treatment residuals have a more promising prospect as a slow release fertiliser than red mud residuals, and our future research will be to further validate this finding on a longer term basis and at a larger scale.

John Murnane
School of Engineering, University of Limerick, Ireland

Publication

Soil phosphorus dynamics following land application of unsaturated and partially saturated red mud and water treatment residuals
J R B Brennan G Murnane N Sharpley,他rron, K R Brye, T Simmons
J Environ Manage. 2019 Oct 15

Read offline:

Related Articles:

	Soil and water bioengineering – Sustainable erosion…Accelerated soil erosion and loss is a serious environmental problem, particularly for the Mediterranean region, due to its long history of human pressures, seasonally contrasting climate and rugged topography. Anthropogenic…
	Interactive/combined effects of climate change and…Both climate change and pollutants are a global problem and a major threat to social, economic, and environmental sectors. Climate change stressors are rise in temperatures, ocean acidification (decrease in…
	Global climate change and mental healthIn the past decade, several empirical studies and systematic reviews of the literature have documented the mental health impacts of global climate change. However, the range of impacts and their…
	Chicago data suggests light pollution disrupts animals’…Population growth, economic development, and urbanization mean more ecosystems are lit throughout the night. Ecologists and astronomers, among other concerned folks, have been raising the alarm that “ecological light pollution”…
	Sheath blight of rice: challenges and managementRice (Oryza sativa L) is one of the most widely consumed cereal crops, grown in more than a hundred countries. Around 40,000 different varieties of rice exist in the world,…
	Atmospheric and genetic parameters influence Rhinovirus…Rhinoviruses are a diverse set of very small and common viruses, repeatedly infecting humans in the course of a single year. For most people, infection usually results in mild common…