The so-called “Golden Goose,” Lake Atitlan is variously insulted by farm runoffs, landslides, garbage and sewage.
At first glance it appears chemical run off would be easy enough grievance to check off the list. But, alas, phosphates and nitrogen, though officially outlawed, are supplied by the government.
Anti landslide measures- like reforestation -are unable to keep up with hurricanes and wildcat building.
Solid waste and trash disposal are utterly dependent on iffy roads and bridges.
So, by default, the easiest to remedy must be Sewage Treatment.
The former Sewage Treatment Plant (STP) was decommissioned by Hurricane Stan when rains killed at least 1500 people and wiped out entire towns. Floods and mudslides inflicted physical damages around Lake Atitlan. And, one day, the enraged river undermined Panajachel’s 1990’s vintage Sewage Treatment Plant. That was six years ago, the replacement plant is still under construction up river from where the old structure came to rest. Building any STP on volcanic soil is like trying to build a swimming pool on Rice Crispys.
Most STP’s are not well suited for jagged karst topography, either. The larger the capacity the less well they will do. STP’s sit atop a land of glorious waterfalls and springs. That water makes way through underground tubes and makes pools in caves. In a drought or in case a feeder stream gets rerouted, the lacy under structures can collapse. This is called a sinkhole. Additionally, while rich in nutrients, volcanic soils are mostly sand – tiny, shiny glass shards. In fact, this soil is so brittle it pulverizes under pressure making it a poor choice for mixing with cement. Over time, small and chronic breakages destabilize materials and that undermines the integrity of a structure.
Getting sufficient land is not done under the police powers of zoning. — far from employing orderly eminent domain procedures, acquiring land for sanitation or any public works is an opportunity for a seller to scalp the Municipality.
STP’s are designed for maximum land use. Their pools and tanks are built close together. But, this necessity focuses a lot of water weight in a small area. UASB (Upflow Anerobic Sludge Blanket) technology requires a series of shallow lagoons. The volume and number of these rectangular feeder pools is driven by the shape of the site and the size of population served. Gravity drains collect pool sludge into an aerated cylindrical tank – diameter and depth driven by the same variables.
In a properly functioning UASB plant, bio-gas can be harvested to power the facility.
NOTE: Gas is naturally produced from bio-wastes and could simply be flared – but, capturing it is cost effective. Current “Best Practice” has the cement cylinder fitted with a “pre-fab” liners – the liner installation needs to be “spot on; balls accurate” to avoid wobbling which would cause a poor seal. Obviously if the gas capturing apparatus has a loose or improper fit it wastes a usable bi-product and could pose an immediate danger.
It is quite possible that the replacement plant’s technology is deficient. In their paper “UASB Technology-Expectations and Reality” Tare and Nema point out flaws in using UASB for sewage treatment – as opposed to processing more fiber rich industrial wastes.
NOTE: As discharges decompose they extract oxygen. So, major objective of conventional wastewater treatment is to dilute and reduce the biochemical oxygen demand (BOD) so that the oxygen content of the receiving water body will not be reduced…
In their study of 9 UASBs the authors found that these plants required an additional “finishing pond” or chemical treatments to have an acceptable BOD.
NOTE: Poo-Gloo’s nested aerators could increase the capacity of these ponds (see Resources.)
“UASB is found to be very effective on high strength industrial effluent. distilleries, pulp and paper plants and food processing.” These high organic loads allow for the capture of enough excess biogas that they pay for themselves in three years. The bi-products of human wastes were not as good as for the industrial masses. We can assume that Panajachel’s biogas yields are probably less than 30% of expected production and we know that there were no buyers for the sludge as fertilizer. So, far from being a profit center the Jucanya plant might require supplementary diesel to run and probably have to pay to dispose of the sludge as well.
Despite the technology’s draw backs and the site’s unfortunate geology, a replacement UASB STP is currently (and at last) being built 50 feet upstream from where the prior plant crumbled down the cliff.
The replacement STP site looks slightly bigger than the prior one. But, unlike the prior plant, the replacement STP’s floor has been dug down 15-20’ below grade to just about 10’ off the river bed. There is a ramp for vehicles and the plant’s vessels are stepped back away from the river. It looks like the neck of the countersunk cylinder will sit about 5’ above the finished floor and the tops of the pools, on their elevated plateau, will sit about 15’ above the finished floor. The entire plant is protected river side by parallel bulwarking. This is a cement filled 1-2’ wide 15’ high gabion berm sunk about 7’ below and parallel to the bed about 10 feet from separate it from the ramp. There are ongoing efforts rerouting the river by dredging a trough, banking and stacking gabions. I mention this because this plant was probably designed before the river taming measures were conceived. So the effects of the bulwark and moat are yet to be seen. Because of the possibility of plant acting as an up river dam and because of the wild streams upland of the plant, it might be prudent for the plant’s neighbors to shore up their adjacent fields on their stream and river sides.
There are multiple alternatives to STP including biodigesters. But, then, there is a balance to be struck between owning and maintaining a septic or other system and relying on public works. Considering that Mayans do not take kindly to utility bills providing individual installations may or may not be a good thing – some training and incentive for compliance has to be factored in. Even though the Panajachel community is stuck with one imperfect plant there is an array of new technologies like the Poo-gloos that could be set afloat in a shallow, impermanent ponds and those solar processing ponds could be placed and easily replaced across the lake.
My favorite solution is even fun and an attractive alternative to both to UASB and any other static STP. It is a sewage treatment barge. These floating urban beach barges set sail on the Danube and they are so odor-free that they have swimming pools and restaurants topside.
Here, they could be spud type barges because that craft has telescoping legs and could “anchor” in a protected cove during a hurricane.