Freshwater lake remediation

Tasik Aman lake is a former mining pool turned into a lake for public recreational use. The lake has low water flow and is prone to water quality issues due to run-off from the surrounding catchments.

Tasik Taman Aman, similar to many urban lakes, experience uncontrollable algal and aquatic plant growth in their surface waters as a result of unnaturally large inputs of nitrogen (N) and phosphorous (P) from polluting run-offs. This causes the algae and aquatic plants to bloom and eventually massive die offs occur in the lake, resulting in large quantities of organic matter being deposited to the lake bed.

This organic matter is decomposed, consuming oxygen in the water column and releasing additional N and P back into the water column that will go on to fuel even more algal growth.

Without oxygen at the bottom at all times, beneficial bacteria and insects cannot biodegrade the organic sediment at bed level of the lake. It is important to maintain healthy levels of dissolved oxygen in your lake because the oxygen aids in the breakdown of decaying vegetation and other nutrients that find their way into the water.

Hence a new solution has come to light which would address the problem of algal formation and not just treat the symptom of algal bloom. This solution is in the form of a product named AQUA-Cal+, developed by the company Calix, a multi-award-winning Australian technology company that is developing new processes and materials to solve global challenges.

AQUA-Cal+ is a special formulated high surface area Magnesium Hydroxide and enhanced with Calcium that acts to improve the overall water quality while delivering a number of unique properties to protect and enhance the lake conditions. AQUA-Cal+ is non toxic, non-corrosive, safe to handle and environmentally friendly.

We had some challenges during the treatment, mainly the control of algae and the increase of pH up to almost 9, due to the buffering effect of AQUA-Cal+. AQUA-Cal+ may have provided more water column space for the fish to thrive but the struvite reaction in an eutrophic lake with very little flushing and continuous runoff input does not help in the control of the algal bloom. It is unavoidable that AQUA-Cal+ needs to be complemented by usage of beneficial bacteria.

Our aim over the next 5-6 years is to restore Tasik Taman Aman’s ability to sustain itself under the continued burden of nutrient overloading. If we can restore the lake’s nutrient cleaning mechanism which diverts nutrients into a healthy ecosystem, sustainability is achieved. Unfortunately, most commonly used lake restoration/rehabilation strategies are not restorative. They treat the symptoms of the lake ecosystem decline without fixing the issue with the system in the first place. Restoring the lake’s nutrient conversation system seems to be the right solution. This, will not only repair the damage caused by nutrient overloading but also help ensure the lake can sustain itself sustainably in the future.

Over the past year of water treatment, there has been a large improvement in lab-based water quality metrics. Biochemical oxygen demand (BOD) and chemical oxygen demand (COD) have decreased throughout the year and have dropped to as low as 3 and 13 mg/L respectively. Total dissolved solids (TDS) has markedly reduced since baseline conditions.

Using the interim water quality index (WQI) published by The Department of Environment (DOE), we can compare the overall WQI of the water standing in the lake from baseline conditions to present conditions.

Baseline WQI was calculated to be 51.6 which is considered a “Polluted” water body. This was driven by very poor oxygen conditions throughout the water column as well as generally high BOD and COD. Present oxygen conditions are much better as are the present BOD and COD. Now the WQI is calculated to be 92.4 or considered a “Clean” water body according to those standards. From over twelve months of monitoring the lake’s treatment progress, we can confidently say that conditions have indeed improved beyond expectation.