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Preventing duckweed, chlydophera and other algae

Putting a stop to green ponds, lakes and dams

The reason for the proliferation of algae is largely due to the presence of above average concentrations of Nitrates and Phosphates. Algal spores bloom forming a floating blanket that prevents the uptake of oxygen by the reduced water surface area. To clean up a body of algae-infested water a healthy population of avaricious bacteria is needed to metabolize these radicals back into the natural food chain.


CH: duckweed dam  Small lake covered in algae


A classic example was noted recently in the maturation river of a small town Wastewater Treatment Works. The constant flow of nutrient rich water, exacerbated by a sludge spill from the reactor, set up conditions favourable to duckweed, which rapidly covered 95% of the river's surface. This meant that the wastewater could no longer 'mature' as the river had turned anaerobic to the extent that the final 'polishing' of impurities from the flow could no longer take place.

BIO-SYSTEMS was called upon to assist. This we did by first remedying the depleted activity in the reactor. We then inoculated the river which was 70m long by 30m wide and separated into 23 x 3m wide channels (see below). The final quality was outside the standard and unfit for discharge (COD 146ppm and both Nitrate and Phosphate values in excess of what is permitted). 1kg of BIO-SYSTEMS B504 was rehydrated in two 20lt buckets of water drawn from the river and slowly fed into the inflow at the rate of one bucket over 10 minutes.


CH: duckweed rampant  Before: duckweed rampant


This ensured a reasonably even distribution, carried by the inflow current in and under the duckweed in the first two channels. We then bowled a further 2kg of B504 into the first and second thirds of the river, the soluble pouches permitting inoculation without getting horribly wet.

After a few weeks, we revisited the site and the improvement was most gratifying. More importantly, the final discharge was back to its previous excellent quality – almost the crystal sparkle associated with a fresh mountain stream.


CH: duckweed cleared  After: how a maturation river should look


Since our treatment, a minor infestation of duckweed is recurring. This is due to the fact that the effluent is carrying excess Phosphates (from laundry powders), a phenomenon that is shared by most Wastewater Treatment Works. It makes sense, therefore, to inoculate (into the final clarifyer is best) a small amount of B504 and BIO-SYSTEMS B250 blend (about 1kg per month). The B250 will degrade the excess FOG present in most works due to overload and maintain the desired final quality.

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