Chapter 19: Liquid Effluent

Effective Date: July 1, 1997 (Issue No. 2)

Last Updated: September, 2023

A. Introduction

All liquid effluents from the University laboratories, office areas and staff quarters enter the HKUST sanitary sewer system. The standards that pertain to these effluents are set by the Environmental Protection Department and apply to all sewers leading into government sewage treatment plants. HKUST is licensed by the EPD to use the sewage system leading to the Junk Bay sewage treatment plant and must conform to the terms and conditions of the license. Regular sampling of the sewage waste stream is conducted by HSEO at various monitoring points. These samples are analyzed for all the parameters required by the license. The results of the laboratory analyses are provided to the EPD in regular reports. Unless otherwise specified, hazardous materials must not be disposed into the sewer system. Details of the HKUST hazardous material management scheme are summarized in Chapter 16 (Hazardous Waste Management).

The legal conditions that govern liquid effluent discharged into drainage and sewerage systems, and inland and coastal waters of Hong Kong are given in the Hong Kong Water Pollution Control Ordinance, Cap 358, S21. Details of the ordinance are summarized in the Technical Memorandum on Effluent Standards issued by the Secretary for Planning, Environment and Lands under Section 21(1) of the Water Pollution Control (Amendment) Ordinance 1990.

 

B. Hong Kong Regulations

I. Standards for Effluent Discharged to Foul Sewers

The current standards for effluent leading to Government sewage treatment plants are listed below:

Parameter	Unit	Upper Limit
pH	pH	6-10
5 day Biochemical Oxygen Demand	mg/l	800
Chemical Oxygen Demand	mg l	2000
Suspended Solids	mg/l	800
Total Toxic Metals	mg/l	1
Phenols	mg/l	0.1
Total Nitrogen	mg/l	100
Total Phosphorous	mg/l	25
Surfactants	mg/l	25
Oil & Grease	mg/l	20
Barium	mg/l	0.4
Boron	mg/l	0.4
Cadmium	mg/l	0.001
Chromium	mg/l	0.1
Copper	mg/l	1
Iron	mg/l	1.5
Mercury	mg/l	0.001
Nickel	mg/l	0.6
Silver	mg/l	0.6
Zinc	mg/l	0.6
Other toxic metals, individually	mg/l	0.1
Cyanide	mg/l	0.06
Sulphide	mg/l	1
Sulphate	mg/l	600

 

 

The current list of “toxic metals” provided by the EPD for sewer effluent includes antimony, arsenic, beryllium, cadmium, chromium, copper, lead, mercury, nickel, selenium, silver, thallium and vanadium.

The license also states that the sewer discharge shall not contain any other matters such as PAH (Polyaromatic hydrocarbons), PCB (Polychlorinated biphenyls), fumigant, pesticide and toxicants, flammable or toxic solvents, biocide, contaminated condensing or cooling water, chlorinated hydrocarbons, organic solvents, petroleum oil or tar, calcium carbide, sludge, floatable substances or solids larger than 10 mm, waste liable to form scum deposits or discoloration in any part of waters of Hong Kong, any substance of a nature and quantity likely to damage the sewer or to interfere with the free flow of its content or any of the waste water treatment processes or to pollute waters of Hong Kong or to injure any sewer worker or equipment. The discharge of any radioactive substances has to comply with the conditions as set out by the Radiation Board.

The Authority will not allow dilution as a means of meeting effluent standards. Dilution lowers the concentration of waste by increasing the volume, but the total mass of waste, and thus the loading on the receiving waters and their biota, do not change.

 

II. Standards for Discharge from the Seawater Pump House

A license that permits HKUST to draw, use and discharge seawater back into the Port Shelter Water Control Zone was granted under Section 20 of the Water Pollution Control Ordinance. The license permits use of the seawater in the heat exchange system of the HKUST seawater pump house and allows treatment of the water by chlorination.

The standards that apply to all effluents discharged into the coastal waters of Port Shelter are also indicated here.

Parameter	Unit	Upper Limit
Colour	Lovibond unit (25 mm cell length)	1
Suspended Solids	mg per litre	15
Biochemical Oxygen Demand	“	10
Oil & Grease	“	10
Barium	“	0.2
Boron	“	0.2
Cadmium	“	0.001
Iron	“	0.6
Other Toxic Metals (individually)	“	0.1
Total Toxic Metals	“	0.1
Cyanide	“	0.01
Phenols	“	0.1
Sulfide	“	0.5
Total Nitrogen	“	10
Total Phosphorous	“	5
E. coli	Count/100 ml	1000

 

 

Other prohibited substances for effluent to coastal waters are:

•  polychlorinated biphenyls (PCB)
•  polyaromatic hydrocarbon (PAH)
•  fumigant, pesticide or toxicant
•  radioactive substances
•  chlorinated hydrocarbons
•  flammable or toxic solvents
•  petroleum oil or tar
•  calcium carbide
•  wastes liable to form scum, deposits or discolouration
•  sludge, floatable substances or solids larger than 10 mm

As with waste water, the Authority will not allow dilution as a means of meeting effluent standards. That would cause excessive loading on the receiving waters and their biological systems.

 

III. Standards for Storm Water Drains

Most storm water drains discharge directly into inland or coastal waters. The Authority will not normally allow discharge of effluent to them. If an exception is made, effluent to them must meet the standards for the next receiving waters downstream. HKUST has waters that discharge into storm drains from runoff during rain storms from buildings, grounds and roads. Water draining from the roof of the academic buildings, where many exhaust ducts ventilate, also goes into storm water drains.

 

C. Practice on Effluent at HKUST

Because of the legal conditions governing the waste water stream from HKUST, students, technicians and researchers must be careful to avoid putting any solid or liquid chemical waste into the sinks that lead to the sanitary sewer system. Guidelines for good hazardous waste practice are given in Chapter 16. From there it can be seen that only simple alkalis and acids that have been neutralized to the pH range of 6-10 can be disposed into the sewer system. All other materials should be disposed of by appropriate hazardous waste procedures (see Chapter 16, Hazardous Waste Management).

Strict guidelines also control the cooling sea water used by HKUST. Chlorination to prevent growth of marine biota within the liquid conduit system is permitted in the licensing agreement as is the periodic use of an EPD registered biocide in the intake system to prevent proliferation of marine growth that would restrict the water intake.

In the case of each waste stream, HSEO conducts regular monitoring and complete chemical analysis of samples to verify compliance with EPD regulations. Records of such monitoring are provided to the EPD for review and are kept on file by HSEO. HSEO also conducts periodic evaluation of the sewage line in the tunnel to Junk Bay and measures stream flow in the pipe at an access point in the tunnel. Periodic EPD inspections of the pipe and verification of the flow are hosted by HSEO.