African expert: mine water can be used to grow biofuels

Experts on natural resource management in the developing world are analysing ways to integrate biofuel production with other activities, most notably mining operations. Earlier we referred to the potential of energy plantations to function as bioremediation components on polluted and degraded industrial sites (earlier post on phytoremediation of coal-bed methane water, and on turning brownfields into greenfields using, for example, miscanthus). When grown on mining sites, biofuel crops - which are not grown for human consumption - can do several things at the same time: they clean up water resources, contain the spread of fine and dangerous particles which affect people living in the vicinity and halt progressive erosion (earlier post). Using degraded mining sites means no valuable agricultural land is taken up.

Now one of South Africa’s most perseverant proponents of biofuels, Dr Robbie Robinson, says that there are many other ways in which the African mining industry can contribute to the production of biofuels. He has developed a number of concepts, which, if explored further, could result in downstream agricultural opportunities.

Robinson has combined the targets of sustainability and creation of work opportunities with small-lot drip-irrigation farming, which could use water effluents – such as those resulting from mining operations – to produce biofuel crops. Clusters of farms that produce these crops can then contribute their produce to a central facility, where it can be processed into biofuels. Robinson thinks that the capacity for biofuel crop production in small-lot farming is surprisingly large.

His calculations show that the creation of 1 million much needed agricultural jobs and the production of 40% of South Africa’s fuel requirements are not beyond the bounds of possibility. Achieving these targets will require irrigation water, which, although much less than is used by conventional agriculture, is still in the order of 5 billion litres a day.

The mining industry produces millions of litres of water effluent every day, which can contribute to meeting the requirements of drip irrigation. Moreover, the mining industry’s logistics and organisation capabilities can also play a meaningful part in Robinson’s concept for the production of biofuels:

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Robinson explains that, although the proposed farming method does not require a high level of skills and is suitable for all ages, male or female, there has to be supervision, discipline and direction. “For more than a century, the mining industry has shown that it is a master in achieving such coordination.

“And in the new climate of sustainability in terms of the Mining Charter, it should be willing and adept at starting the evolution of such cluster farming concepts,” Robinson says.

He points out that all mines are required to handle large quantities of water To obtain the water needed by their operations, some mines pump water over great distances, while others use nearby river water.

Others also have to pump out water draining into their mines to prevent flooding.

All have to dispose of an aqueous effluent. Robinson says that, on the Witwatersrand and the adjacent coal-mining areas, the influx of water into the mines even after mine closure causes problems in the formation of acid mine drainage (AMD).

“The age-old solution of evaporation on slimes dams is no longer tenable environmentally. “There have been many propo- sals for treating the AMD to produce much needed domestic water, for example, but the most cost-effective is to treat it to produce agricultural water which is ideal for drip-irrigation farming.” Hence, he believes that the concept of cluster farms near such mines to produce biofuels and food products using mine personnel or the associated community is well worth more detailed examination. There are several instances of using dolo- mitic underground water from gold mines for drip irrigation using waste mine land since a feature of this method is that high-quality agricultural land is not needed.

By far the most productive application of small-plot farming for biofuels – which will ensure the highest income levels for farmers – is in the high temperature, no-frost regions, such as in KwaZulu-Natal and Mpumalanga. Robinson says that these are generally areas that are short of water.

“Although there are mines in these areas, such as at the Palaborwa copper mine, which could develop biofuel clusters, the capacity of the area is much greater and the demand for work opportunities much higher. “Hence, the concept of gravitating water effluents from the Highveld areas surrounding Gauteng is interesting. “If the treated AMD or domestic effluent were to be conveyed by pipeline to the Crocodile or Olifants river valleys, useful off-peak power could also be generated by modern hydropower stations,” he adds.

Drip irrigation and cluster farming Robinson’s drip irrigation system comprises a continuous planting and harvesting regime in which maize is grown in rows, using tubular, subsurface drip irrigation along the horizontal width of each plot. Initially, a complete sequence of crops is established at different stages of growth.

Every day the farmer will plant one row of the crop with a newly-placed drip tube and, at the other end of the plot where the crop is fully grown, a row will be harvested and the old tube removed for cleaning or re-extrusion.

In this way, a cluster of farmers will be able to supply a central bio-fuel production plant with feedstock throughout the year.

Social benefits
The advantages of the system include the fact that, once established, the farmer receives a continuous income.

While the system is regarded as too labour-intensive to be implemented abroad, Robinson says that it is suited to South Africa, where rural unemployment is estimated to be as high as 40%.

Drip irrigation will enable the best use of scarce water resources. “Research in Australia has indicated that drip irrigation is 85% efficient in terms of meeting the plant transpiration requirements, as compared with 15% efficiency for the best centre-pivot irrigation,” says Robinson.

No high-quality agricultural land is involved and for the hypothetical million farmers, a land area of about 200 000 ha is contemplated. About 100 t/y of maize can be produced from a group of small-lot farmers occupying one hectare by using the system of unbroken planting and harvesting combined with drip irrigation. Robinson first started to investigate the possibility of bioethanol production in 1978 while directing Sentrachem’s research.

While he has been promoting the concept ever since, it has not been rolled out commercially in South Africa.

“Many sceptics have told me that it is a pipe dream, and that it will never be realised, and I must agree that none of the estimates have been demonstrated in practice. They were intended to be illustrative rather than proven.

“However, no one has challenged the basis of my calculations.

“In terms of the most urgent priority in South Africa, namely creation of jobs in impoverished rural areas, I believe it is well worthwhile to start some experiments,” he says.

And in a world where green energy shortages are becoming more severe, and carbon credits are becoming increasingly popular, there could be significant potential in taking up Robinson’s proposal.