Bamboo as a filtering medium

Bamboo as a filtering medium in the control of effluent and excess soil nutrients pollution.

The essence of all sewage and effluent treatments is to physically separate dissolved, suspended and floating inclusions from the water base. Sludge tanks, screens and centrifuges can remove much of the solid waste. Induced chemical reactions may serve to precipitate further foreign matter and so render it accessible to screening. Ultimately, the strained liquid is exposed to biological agents for the safe conversion of the dissolved pollutants into filterable inert residues.

The results of successful biological interaction generally lead to either additional recoverable solid wastes or to gaseous compounds easily dissipated by agitation and ventilation. Inevitably, most water treatment managers seek to release treated effluent from their care at the earliest stage that opportunity, regulation, funding or conscience allows.

Biological exposure may vary from the crude spraying of diluted human and animal sewage directly onto pasture through to very complex, multiple stage processing plants. The direct spraying of nominally treated wastes is an ancient and quite acceptable agricultural practice providing necessary care and understanding are applied to ensure that the water-borne pollutants are indeed capable of being fully broken down before the residual water is taken back once again back into the natural drainage and groundwater systems. It is very much a question of establishing a balance between concentration and dissipation.   

Land, for example, that is sprayed with piggery effluent will very soon become "pig-sick" if the rate of natural biological breakdown in the soil is overtaken by the rate of effluent deposition. Pasture growth falls off, the risk of animal disease escalates alarmingly and neighbourliness plummets. Rainfall, temperature and the phase of seasonal growth obviously have a variable and controlling influence. There is also the danger that certain elements, harmless in low concentrations, may over time accumulate to toxic proportions and be subsequently incorporated into some form of harvested crop or inadvertently released back into the water supplies.                  

Certain prerequisites must therefore be satisfied before irrigation with partially treated effluents should be contemplated.

1. The area over which spraying is to take place must heavily err on the generous side if natural precipitation and flooding are not to be allowed to interrupt spraying.
2. Land utilisation must not be such that effluent residues can find themselves either directly or indirectly in the human food chain.
3. The vegetation and soil, in combination, must have the capacity to arrest, absorb and convert all the non-water components as well as controlling the rate and impact of water transfer.

The first parameter to be considered is that of site: size in relation to the volume of effluent to be treated, proximity to the effluent source, limitations imposed by planned or existing utilisation, the nature of the soil and the characteristics of the water table. If some produce is to be gleaned from the irrigated land then suitable access for maintenance and harvesting and a workable proximity to markets are necessary further considerations.  

The system design must first address those basic water management issues raised by any normal irrigation project. The means and cost of delivery, of dispersion, drainage and maintenance.                 

Finally, the determination of the nature of the intended vegetation - natural or farmed - is critical to the success of the venture.                

Contemporary society recognizes the need to safely convert industrial as well as sewerage wastes. Experiments have been conducted in Australia to accommodate the effluent from mechanical process pulp mills by spraying it into pine plantations destined to become feedstock for the same mill. This is an elegant solution. The improved growth of the trees brought about by  irrigation naturally boosts the productivity of the plantation whilst at the same time accommodating both effluent disposal and the provision of a locally valuable product that is independent of the food chain. Trial plots have been studied, judged successful and expanded. 

Well, if it all works so well why bother to introduce bamboo at all?  Simply, it can be made to work even better still. There are of course as many different applications as there are problem effluents. But consider the pulp mill situation referred to above.

1. Pine trees may take up to fifteen years or more before they are ready to harvest. That is a lot of pumped irrigation and a very long investment time in capital plant and maintenance before a tangible return can be realised. Bamboo may be cropped after only three years and may then be regularly, annually harvested without having to destroy the original plantation or the soil covering as is normally the case with softwood felling.
2. Compared with softwood trees, bamboo's faster accumulation of biomass combined with the advantage of an annual cropping cycle commencing only three years after initial planting means that much smaller areas of plantation are required to satisfy both the need for effluent disposal and feedstock production. Capital and maintenance costs are correspondingly reduced.         
3. Demand for paper products, although showing a progressive upward trend, does fluctuate over time especially with regard to particular products and the impact of unforeseen competition. Tree plantations, locked into a minimum of fifteen but sometimes a thirty year cycle, create a vulnerable inflexibility for the industry. The versatility introduced by a three year cycle means that bamboos of different characteristics can be established to fill new requirements or existing plantations manageably expanded to satisfy an expanding market.
4. With so many fast growing, large, tropical bamboo species acclimatised here their enhanced production, say, in comparison with the slower growing pines in cooler regional climates means that the cost of pulp may be maintained at not only a viable but, indeed, at an internationally competitive level.

 Bamboo as a source of paper pulp has no history in Australia. Both India and China use bamboo extensively although, in deference to the ready availability of process know-how and machinery from the West, both might well perhaps prefer to have easy and economical access to softwood trees. But they have no such access so must apply themselves to a prolific resource that is much more readily obtained. In this they mirror the endeavours of our own early paper manufacturing industry which only reluctantly turned to softwood feedstock a little more than a century ago and, far more recently still, learned to employ eucalypts for pulping.                 

Prior to the Second World War, eucalypts were quite unsuitable for pulping according to the papermaking establishment. A little adversity, a shortage here, a price increase there and guess what? Yes, a breakthrough - "eucalypt" is the wonder tree exported around the world! So it will be with bamboo: too hard today because we have a naturally growing alternative, indispensable tomorrow when that forest resource becomes increasingly difficult to harvest and pine plantations fail to meet the financial returns obtained by cultivated bamboo.                 

Overseas experience indicates that mixed stands of trees and bamboos can provide benefits to the growth performance of both. Certainly this is something that should be tried here especially within a waste water treatment project. Reports show that the interaction of different plant storeys and the more complete ground cover has substantial and beneficial effect upon ground temperature, frost incidence, humidity as well as an increase of biomass and ground litter. The shallow rooting habit of bamboo complements deeper tree root systems to uplift the maximum amount of nutrients from the soil. Such dual planting also suppresses weed proliferation, accelerating the growth of each component. The diameter, height and straightness of both timbers have been shown to be substantially enhanced whilst the inhibition of side branching provides a natural and beneficial pruning.

Not all pollution problems are associated with toxic outpourings from residential and industrial complexes. The serious and continuing hazard of blue-green algae in our waterways highlights the need for an effective, passive but continuing deterrent to that concentration of soil nutrients which has been identified as encouraging algae growth.  In this application irrigation water may not be either freely available or economically feasible to provide. Hardy and vigorous plants that can proliferate in a range of conditions, and by so doing take up and retain within their biomass the nitrates and phosphates already in the soil, must therefore be provided. If, in addition a worthwhile crop can be harvested from such plants  then all the better for, by this self-financing means, incorporated nutrients are progressively removed from the area. Of course, bamboo!

The Chinese forester makes automatic recourse to bamboo when putting in place soil erosion and water catchment protection schemes. An assurance based on generations of experience allows, without further debate, the planting of thousands of acres in hundreds of projects along vital waterways throughout China. In Australia, ignorance all too often gives rise to rejection. Quite apart from the arrogance implied by our disbelief of generations of human practical, tangible and visible accomplishment, the reluctance of local authorities in Australia to trial bamboo as a protective soil cover even in the most demanding and urgent of situations signifies a general lack of both intellectual curiosity and self confidence that bodes ill for this nation's future.

At the forefront of this insular thinking is, surprisingly enough, the formally trained farming and environment professional. Of course, we are all of us familiar with the errant bamboo in the backyard but we are not talking backyards here but critical waterways whose banks are scored by erosion and streams poisoned by excess nutrient wash. Also, and quite understandably, no scientist is keen to gain the same kind of fame as attaches to the original promoters of the cane toad. However, responsible caution is one thing, narrow parochial refusal to acknowledge well researched and proven practices quite another.

The qualities of bamboo that incite opposition are its rapid growth and dense root matrix, yet these are exactly those characteristics that are essential for effective soil protection and conditioning. A rapid accumulation of biomass, evergreen canopy, ample ground litter, vigourous surface root extension and general hardiness are mandatory whether it is bamboo or some hitherto undiscovered Australian native that is to be employed. It is to the advantage of bamboo that it does not spread by uncontrollable seed dispersal, it cannot invade or block. water channels and is not poisonous to either native or domestic animals. Moreover, mature stands can be successfully and regularly cropped for economically valuable timber and for edible vegetable shoots without the slightest interruption of the soil binding role. No Australian native can meet this demanding specification.             

Research in India has demonstrated that for one common species of bamboo the potential for nitrogen uptake was such that, when made freely available, culm yield increased by 15 times - not 15 percent but multiplied by fifteen! The research confirmed that nitrogen had the greatest influence on growth and biomass production closely followed by potassium. Phosphorus showed a marked influence only in conjunction with nitrogen. As is to be expected from the variety of habitats naturally occupied by bamboo, different species have quite distinct appetites when it comes to nutrient uptake. There is the potential therefore for a close matching of plant and circumstance when setting out to arrest excess nutrient contamination.                 

In Yunnan and Fujian provinces of south east China, capital intensive, professionally engineered river bank protection schemes proved less successful during a period of extreme weather conditions than did adjacent natural bamboo groves prompting authorities there to speed up and extend their re-afforestation programs in water catchment and river systems.   Similar experience in Japan has shown that even heavy flooding and the damage caused by floating debris will not deter the rapid regrowth of bamboo. Indeed, flood damaged areas responded with an above average growth in the following two seasons.

Contrary to superficial opinion, bamboo need not expand indefinitely to become in turn a menace but can be contained providing the species and situation are properly matched at the outset. What we badly need in Australia is a Shire Council with the resolve to address the problem (backed by the relevant research and academic institutions suitably purged of parochial botanists) to trial bamboo plantations on a workable scale so as to reproduce here the findings of overseas communities.  The rewards for such an endeavour may well extend beyond the necessary but isolated objective of nutrient uptake. Bamboos planted for this purpose can also provide income and employment to rural communities by the sale of harvested products as well as from such secondary manufacturing activities that bamboo plantations of sufficient scale universally generate. Just as importantly, bamboo will curb soil erosion and, if so desired, provide in time an effective natural barrier to prevent the passage of cattle and further damage to the banks of waterways.

Durnford Dart - September 1994