HWT (Pty) Ltd

WATER & EFFLUENT TREATMENT ENGINEERING HWT (Pty) Ltd

94 0190 07 PO Box 28 • Lynedoch • 7603 • South Africa

E Mail: hwt@iafrica.com FAX: +27 (086) 688 2069 TEL: +27 (021) 881 3014

Trickling SOG filter sewage treatment For treatment of sewage from individual households, HWT has developed an efficient and low energy treatment plant. The SOG trickling filter is a sewage treatment process that has evolved from the need to treat small and intermittent volumes of domestic sewage.

Unlike most conventional sewage treatment plants, the SOG filter makes use of earthworms, fungus and bacteria to treat sewage. By spreading the type of organism activity, a larger range of variable flow and load is possible. The range in size of treatment organism also facilitates the conversion of sewage to heat and gas as opposed to mere biomass. In the SOG filter there are pockets of aerobic, anoxic and anaerobic zones. Organisms live in the various zones performing selective functions including dissolved organic material degradation (COD reduction), conversion of ammonia to nitrate (nitrification) and removal of nitrate (denitrification). In conjunction with the presence of various habitats, the SOG filter makes use of media that has adsorptive properties. Portions of dissolved organic material are trapped in the media. In times of low or no flow, the trapped material becomes available as a food source (substrate) for organisms that thrive on sewage. If no flow conditions persist, the organisms will consume all available and trapped substrate. When flow recommences, the media will adsorb substrate and allow the concomitant regrowth of organisms. Sewage treatment using a trickling SOG filter is a passive process. Raw sewage is collected in a septic tank/ solids separation arrangement. The settled sewage is collected in a pump sump and simply discharged to the top of the trickling SOG filter. Sewage works its way through the filter media, which is housed in layers, and is collected at the base of the filter. From this point, the treated water can be directed to a re-use option such as irrigation pump or gravity discharge arrangement.

HWT (Pty) Ltd

Biological waste water treatment Waste water description Domestic waste water tends to have a variable flow and organic load. The conductivity of the waste water is a function of chemicals used in the house and this too is variable. The National Water Act of 1999 (Currently under review) currently makes a distinction between discharge to a water resource and disposal via kikuyu irrigation. For both disposal routes emphasis is placed on sustainable reuse of the water. Irrigation is therefore a primary objective in the treatment of waste water. From our experience, removal of the waste water organic load is the most capital intensive. Conductivity is best achieved by judicious use of chemicals. Organic load in waste water is analogous to sugar in coffee. It cannot be filtered out with conventional filtration. Like sugar it is biodegradable and can be removed successfully in a carefully designed biological environment. Treatment Options

Waste water is collected at a solids separation tank. Overflow from this tank is directed to a suitably located flow balancing tank and pump sump arrangement. Solids free effluent is pumped to the SOG trickling filter which comprises 4 layers of suitably sized crates. The number of crates required is a function of the flow and loading rate.

Organic treatment of the solids free waste water takes place in a mixed media biological filter. Waste water is evenly distributed above the filter where after it percolates through the media taking approximately 48 hours to flow from top to base.

The mixed media hosts a range of organisms including bacteria, fungi and worms. An important component of the mixed media is harvestable sphagnum peat. This type of waste water treatment has been widely used in Canada and Ireland.

The treated water, compliant with the , is collected in a sump for re-use. DWS General or Irrigation Standard

Trickling SOG filter – low energy and highly effective. This unit treats up to 1000 litres per day

Samples. After inert solids interceptor on left and post SOG filter on right

HWT (Pty) Ltd

Site layout options

Trickling SOG filter with control panel. Pump sump under manhole cover on right

Trickling SOG filter covered with fygies and indigenous creeper

Trickling SOG filter with pump sumps under manhole covers

HWT (Pty) Ltd

Motivation for installation of the HWT system 1. Proven technology Peat filtration and treatment of sewage has been used for many years in Canada and Ireland. For single dwellings it is a financially viable option. 2. Low energy One pump aerates and transfers water 3. Low visual impact The solids separation tank is constructed below ground level. 4. Low maintenance The treatment plant design centres on ease of use and simplicity. 5. Upgrade considerations A key feature of the design is the provision for upgrade in the event of future growth. The SOG filter geometry is chosen to allow simple addition of a new tank. The control panel includes provision for additional mechanical equipment. 6. Minimal solids handling Solid material in the wastewater is collected in an HWT solids separator. This is a robust and hygienic solids material collection device.

HWT (Pty) Ltd

DEPARTMENT OF WATER AND SANITATION

Discharge limits and conditions set out in the National Water Act, Government Gazette No. 20526, 8 October 1999

Wastewater limit values applicable to discharge of wastewater into a water resource

SUBSTANCE/PARAMETER

GENERAL LIMIT

SPECIAL LIMIT

Faecal Coliforms (per 100 ml) 1 000 0 Chemical Oxygen Demand (mg/l)

75*

30*

pH

5,5-9,5

5,5-7,5

Ammonia (ionised and un-ionised) as Nitrogen (mg/l)

3

2

Nitrate/Nitrite as Nitrogen (mg/l)

15

1,5

Chlorine as Free Chlorine (mg/l)

0,25

0

Suspended Solids (mg/l)

25

10

Electrical Conductivity (mS/m)

70 mS/m above intake to a maximum of 150 mS/m

50 mS/m above background

receiving water, to a maximum of 100 mS/m

Ortho-Phosphate as phosphorous (mg/l)

10

1 (median) and 2,5

(maximum) Fluoride (mg/l)

1

1

Soap, oil or grease (mg/l)

2,5

0

Dissolved Arsenic (mg/l)

0,02

0,01

Dissolved Cadmium

(mg/l)

0,005

0,001

Dissolved Chromium (VI) (mg/l)

0,05

0,02

Dissolved Copper (mg/l)

0,01

0,002

Dissolved Cyanide (mg/l)

0,02

0,01

Dissolved Iron (mg/l)

0,3

0,3

Dissolved Lead (mg/l)

0,01

0,006

Dissolved Manganese (mg/l)

0,1

0,1

Mercury and its compounds (mg/l)

0,005

0,001

Dissolved Selenium (mg/l)

0,02

0,02

Dissolved Zinc (mg/l)

0,1

0,04

Boron (mg/l)

1

0,5

After removal of algae