European researchers hope to increase water efficiency by 80% in the continent’s hugely important olive industry.
The EU is the largest producer of olives in the world, refining 2.2 million tonnes of olive oil from 12,000 olive mills. This is 80% of world production. Prospects for the industry are good, with sales increasing across the world as people learn about the health benefits of olive oil. But while the olive industry is a vital market to Europe, it faces increasing competition from more competitive neighbours, notably from Turkey, Syria and Tunisia. Waste control regulations are also becoming more stringent.
But waste management poses a big problem for the olive industry. Olive processing generates large amounts of polluted liquid wastes, primarily from water used to wash the olives prior to processing.
The quantities of water required are astounding, with 50 litres needed for every 100 kilos of olives. ‘There is a huge amount of water – about five billion litres annually – used in this,’ explains Antonia Lorenzo, coordinator of the Algatec project and a researcher from lead partner BioAzul.
Olive fruit washing is the first step in the oil extraction process, removing impurities accumulated during harvest. That water is then mixed with olive mill wastewaters (OMW). Currently these wastes are either run through a costly treatment process or disposed of in adjacent rivers, where it has a serious environmental impact. Impurities in the wastewater are regarded as having both very high chemical oxygen demand (COD) and biological oxygen demand (BOD), two important water quality indicators. High COD and BOD essentially mean that chemicals and biological material in the water are reacting with oxygen, depleting it rapidly. This can lead to eutrophication in rivers or ground water, with serious consequences for native flora and fauna.
The water also has a large number of suspended solids and phenolic compounds, which are toxic to plants and have an antibacterial effect, which can lead to further negative ecosystem impacts. As such, the wastewater poses a pollution risk for superficial and underground waters. Concentrations of these pollutants in the wastewater can exceed typical domestic water by 200 to 400 times.
It is a big problem, particularly in a highly competitive industry based in more arid regions. A purification system must be found but any solution must effectively deal with the waste at a very low cost.
The Algatec project plans to deliver an economic and effective system through an elegant combination of promising biotechnologies which effectively recycle olive mill wastewater using microalgae. “It is important to stress that this research comes from the project’s SMEs as well as the research institutes,” explains Lorenzo. “‘The idea is based on SME knowledge.”
The Algatec concept works in three steps. First, the water is run through a standard filter, removing most of the suspended solids. The water is then routed to a small and affordable photo-bioreactor that uses microalgae to break down the waste. This is the core treatment process. Photosynthesising microalgae feed on nitrogen, phosphorous and other pollutants present in the olive water and release oxygen. Bacteria absorb the oxygen and produce CO2, a bacterial by-product consumed by the microalgae. Combined, the microalgae and the bacteria work in a symbiotic relationship which, at the same time, dramatically improves the BOD and COD profile of the water. Next, the water is treated using membrane purification technologies. The water is passed through a membrane module, which uses hydrostatic pressure to filter the water coming from the photo-bioreactor through a microfiltration and a nano-filtration unit.
Innovative and competitive
“The use of membrane technology will make the system extremely innovative and economically competitive,’ notes Lorenzo. “In fact, membrane technology currently represents one of the most useful separation techniques because of its low environmental impact and low energy consumption.”
After this final filtration process all that remains is drinking water and a residue to be sent for disposal. The membrane filtration stage purifies the wastewater of all suspended solids. “By the end of the project we aim to achieve recycled water with no odour, no colour, very low COD and total organic carbon of less than 20ppm, no fatty substances, dry residual material of less than 0.5%, low conductivity and a turbidity of less than 0.8 NTU,”remarks Lorenzo.
These are impressively stringent standards. Low conductivity means that there are few dissolved salts in the water, while turbidity is a measure of visual haze or muddiness, and turbidity, or nephlometric turbidity units (NTU), of less than 0.8 qualifies as drinking water. The upshot of all this filtration is that olive mills can recover about 90% of used water simultaneously increasing olive mill water efficiency by 80%.
One of the most elegant aspects of the system is that much of its action is powered by naturally occurring phenomena, such as sunlight to provide energy to the microalgae, which in turn break down pollutants as a happy by-product of their metabolism; the resulting partially treated waters are then passed through a superfine filter using hydrostatic pressure, or gravity. The rest of the system consists of pipes, glass tubes and pumps to route the material through the process.
As such, the Algatec system is powered primarily by ingenuity. That ingenuity is powerful enough to recover and recycle the majority of the drinkable water used in the olive washing process. The project is well on target to achieve its ambitious goals. Partners are homing in on an appropriate microalgae biotechnology. There were 18 strains of bacteria and tywo strains of microalgae have been genetically characterised.
“The most remarkable result is that the consortium has found a combination of algae and bacteria that can grow in polluted water with high phenol concentrations,” said Lorenzo. “This is a breakthrough result.” The consortium has also validated the overall approach, with a prototype photo-bioreactor effectively removing COD and BOD after 30 days, and now experiments are focused on reducing the retention time. ”In addition, we are studying different pre-treatment methods with activated carbon in order to decrease the turbidity of the washing water before it enters the photo-bioreactor, thus favouring algae growth and treatment efficiency,” Lorenzo explains.
In all, the Algatec system offers an impressive solution to one of the sector’s biggest challenges, and undoubtedly it will inspire further research in other water-dependent industries. The Algatec project receives funding from the SME programme of the Sixth Framework Programme (FP6).
Source: Research EU Resulsts Supplement. No 31, February 2011 (http://cordis.europa.eu)
Category: Industrial Water