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Saving septic tanks

How to solve septic tank mismanagement

CH: septic tanks - view


A game lodge in the Pilansberg - a mountainous part of the Transvaal bushveld and home to many wild animals including the Big Five (predators) as well as a huge variety of antelope and bird species - was experiencing problems with their effluent disposal.

Set in a beautiful, scenic setting miles from anywhere, the lodge is made up of approximately 20 four-sleeper thatched rondavels (circular huts), each with its own en-suite bathroom, kitchenette and braai. A reception building boasts amenities such as: an office, internet facilities, a gift and grocery shop, a gymnasium, a swimming pool – with obligatory bar in the lapa (a walled courtyard with a central open fireplace) – an airy lounge with adjoining TV room and a restaurant for those who do not wish to cook for themselves.

CH: Septic tanks - giraffe

The lodge had been doing pretty well for several years; however, problems with their wastewater disposal eventually gave rise to nefarious odours that began chasing their patrons away. The lodge has a 'maintenance man' (let’s call him George) who tried to remedy the problem by pouring bleach and Jeyes Fluid into the offending drains, which were frequently blocked causing evil smelling effluent to overflow onto the pathways. The kitchen drains were the worst. Although George used a couple of kilograms of a proprietary enzyme powder every month, the situation began deteriorating from bad to worse.

BIO-SYSTEMS SA was called on to investigate. We found, by using a tracing dye, that the lodge had seven septic tanks, not just the four that George had advised. We also discovered that two were plumbed in tandem and all of them were considerably undersized: two were plastic 'torpedo' tanks and the other five small brick units of approximately 2.5m3 capacity. Most of the lids were rusted, ill fitting and overgrown with vegetation. The soakaways were in a horrible condition, too. Five of them were linked by a common, now dangerously overgrown, surface channel that discharged into a shallow pan (pond) just inside the boundary fence some 150m from the main complex. The pan attracted mosquitoes, flies and reeked terribly. A case of 'out of sight, out of mind'.

CH: septic tanks - lodge 1  The state of one of the septic tanks before BIO-SYSTEMS intervened

The kitchen did have a grease trap, but it was badly designed and significantly undersized for the load it was carrying: upwards of 60 guest meals, plus 20 staff meals a day. A another quandary was that all the wastewater ran to the septic tanks.

Here was a classic example of the 'blind leading the blind'. Well meaning though they all were, nobody on site knew much about effluent and waste management. While George did his best, he was forever being called away to change lamp bulbs, clean braais, wash cars and fix leaking hoses etc. Ironically all the people concerned were genuinely convinced that they were 'environmentally compliant'.

We put pen to paper and worked out a practical plan to rectify all the wrongs we had found. We calculated that sewage was of the order of 6,500lt per day and grey water would be double that at 13,500lt per day (105 people @ 60lt sewage and 105 @125 lt grey water per day). We had to bear in mind that the nearest well stocked builder’s merchant was in Rustenberg, over 105 km away, so materials were expensive and had to be ordered well in advance.

We suggested lodge management do the following:

Septic Tanks
Clean out and modify the brick tanks, enlarging them to accommodate sewage at 60lt per person per day for 21 days.
We calculated there should be:

  1. One per four rondavels = 4 x 5m3
  2. One for the reception and staff change rooms = 1 x 7.5m3
  3. One for the restaurant staff and guest toilet = 1 x 7.5m3
  4. Provision for signage regarding what to flush down the toilet – many urban visitors were ignorant of the sensitivity of septic systems
  5. Regular, six-monthly inspections and inoculation with BIO-SYSTEMS STR Bulk

CH: septic tanks - eg. 1 

Examples of other septic tank mismanagement


CH: septic tanks - eg. 2


Soakaways
We did away with the existing soakaways because the ground was not really suitable (not sufficiently porous) and lead all the pretreated effluent in 75mm smooth-walled irrigation pipes to a new soakaway – a 50m unit built to BIO-SYSTEMS SA specs (available from info@biosystemssa.co.za). This was dug out on the lower slopes of the enclosed 3ha site, as a temporary measure prior to the installation of a package plant next year (when funding will be available). This was especially important as the lodge relied upon two boreholes within the boundary fence for its drinking water, augmented by some rain in the wet season, and the danger of contamination was imminent.

Grey water
This was a more complex problem, but necessary to reduce the hydraulic load on the septic systems whilst gaining maximum benefit from the resource. Water costs money (electricity) to pump out of the ground and in high summer the flow deteriorates progressively as the limited ground water is tapped by other farms lodges in the area.

We exposed all the outfall shower, bath and basin drains from the rondavels and ran a 50mm u/g pipe in the sewer trenches to a central point on the lower side of the buildings. Here we built a small in-ground sump, using a new 2,000lt plastic septic tank fitted with a Pedrollo Top Vortex submersible pump. The gravity inflow line from the accommodation went through a removable Rhino Filter element to catch hair and grit, while the pump with its own automatic float switch lifted the strained effluent to a 10,000lt surface-mounted treatment tank, disguised by wooden laths covered with a creeper (which bore courgettes for five months of the year!). The treatment tank was fitted with a circulating/transfer well-point pump complete with a 90’ switching manifold valve and a clockwork timer that activated the unit every six hours for four hours, giving five times four-hour cycles per day. On the delivery side of the pump was an AirMix Infusion Injector and the normal cycle was to circulate the water in the treatment tank via the injector, aerating the water. Each week George was to add five level teaspoons of BIO-SYSTEMS Grey Water Additive (GWA) and report any leaks or prolonged silences to the manager. To allow for wet periods, we provided three 5,000lt interconnected storage tanks, also linked to the same circulating pump's manifold so that their contents could be circulated/aerated once or twice a week as necessary.

Toilet Flush
The idea of re-using grey water for this purpose made good economic sense, although the initial cost of materials raised the owner's eyebrow. But the payoff proved to be worth the expense. Polycop pipe was layed in the same sewer trenches and lead to twin, interconnected 200lt plastic drums in the roof spaces – next to the solar geysers – in each rondavel and above the staff quarters.

Irrigation
Every so often, when the storage tanks were almost full, we suggested their contents be pumped to an earth dam on top of a hill behind the lodge from where it could gravity feed to the lodge plantings and herb garden via a manifold, which it irrigated through 2.2lt per hour button drippers.

Our recommendations were accepted, acted upon and implemented over a period of five months. Trenching was done by the back-hoe that came every year to skim, fill depressions and maintain the sand roads around the lodge. All in, the upgrade cost inside of R50k (the income from 33 guests; a payback of approximately three months). The results were gratifying in that the complaints ceased, the effluent quality improved greatly and the staff benefitted from the improved conditions. What's more, the lodge was able to advertise that effluent and waste was disposed of in accordance with international standards.

As far as our products are concerned, a dosing regimen for STR (septic tanks), SAC (soakaways), DF60 (guests' facilities, bathrooms and kitchen drains), B220 (grease trap) and GWA (grey water treatment system) was implemented at a cost averaging R765 + Vat per month.

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