Environmental Challenges and Continuous Improvement
In 2003, all major sewage treatment works performed satisfactorily, meeting and very often achieving better than the licence requirement imposed by the environmental authority. Various difficulties were encountered and subsequently resolved, while new initiatives were introduced to continuous improve the output and outcome of our work. A few examples are highlighted below.

Stonecutters Island Sewage Treatment Works
In 2003, our largest facility Stonecutters Island Sewage Treatment Works treated close to 1.4 million cubic meters of sewage a day, putting it amongst the world's largest operation of its kind. Using Chemical Enhanced Primary Treatment (CEPT) process, the SCISTW achieved an average BOD5 removal efficiency of around 70% and TSS removal efficiency of around 80%, hugely surpassing the designed values of 35% and 70% respectively. By sustaining the highest standards of operation, DSD assured the best possible environmental benefit for Victoria Harbour.

Shatin Sewage Treatment Works
Against an increase of odour complaints, the works took a number of measures to address the situation. This included containment of the odour source by enclosures or covers, dosing chemicals to prevent the formation and release of odour, treating the malodorous gas before emission, and putting in place a monitoring system to measure hydrogen sulphide at strategic locations. Upon these efforts, the air quality in the neighbouring areas improved and the number of odour complaint dropped.

The shortfall in treatment capacity remained to be a challenge. Online sensors were installed to provide instantaneous information on the condition of the reactor tanks. With intensive effort in adjusting reactor conditions, the effluent quality continued to improve in 2003, bringing it in line with the effluent discharge licence conditions by November. Construction of the long term improvement works to provide the much needed capacity was in good progress, with effluent treatment phase of Phase I due for completion in 2004 and Phase II, in 2005.

Shek Wu Hui STW
To save energy, the High Volume and Low Volume Blower Systems were connected up in 2003. Lower air flow is now applied to reactor tanks at low effluent flow period, whereas full flow is applied during peak flow period. It is observed that the unit aeration cost is reduced from $0.158 to $0.138 per m3 of sewage treated, which is equivalent to $584,000/yr. Working on this success and to provide further energy savings, we will install a new LV blower by October 2004 funded under Save and Invest Accounts. This will allow further flexibility to match air supply with flow volume throughout the day, hence achieving power economy.

Yuen Long STW
In 2003, the aged ceramic air diffusers in all aeration tanks were replaced with more efficient membrane type air diffusers. Less air supply is required from the air blowers due to improved oxygen transfer efficiency. This improvement will result in a $0.4M saving in electricity expense each year.

Tai Po Sewage Treatment Works
Significant electricity was saved by channelling effluent into a few reactor tanks during the low intake period at night time. Energy savings was accomplished without affecting effluent compliance. In seeking continuous improvement, an energy audit was carried out in June 2003 with a view to identifying further Energy Management Opportunities.

Mui Wo Sewage Treatment Works
DSD conducted an energy audit in June 2003 joined by EMSD engineers. The main purposes of the audit were:- (1) to identify the major power consumption equipment and recommend feasible energy management opportunity (EMO) with the energy saving forecast; and (2) to apply EMO to improve the efficiency and performance of the plant with the implementation of energy-saving measures. The walk also served as a "train-the-trainer" session where skills from EMSD in energy auditing could pass on and multiply in DSD.

Sewerage works in urban area
Construction and replacement of sewers in the busy urban area poses a unique challenge to DSD. The mitigation of disruption to traffic, air, noise and drainage nuisances is our prime concern. Road openings are reduced to a minimum such as by the use of trenchless methods. Hoardings are placed to separate pedestrians from the work site. Stringent environmental controls are enforced at the site to properly manage dust, odour, noise and muddy drainage. Works duration is shortened to the minimum possible. Communication channels are open to neighbours so that grievances can be attended to and resolved immediately.