Evaluation of pre-treatment method of wastewater at MERAB’s waste treatment facility in Rönneholm

Abstract

In this study the efficiency of a pre-treatment method planned to treat wastewater produced at a waste treatment facility in Rönneholm (Skåne, Southern Sweden) was evaluated. At this waste treatment facility, operated by the publicly owned waste recycling company MERAB, a treatment is needed to lower concentrations of potentially environmentally detrimental contents in the wastewater to an extent which would allow discharge into the environment and/or irrigation of a willow plantation as a tertiary treatment. The planned pre-treatment, consisting of an aeration basin and a sedimentation basin which the wastewater shall pass through subsequently, was simulated in the laboratory. Physicochemical properties as well as concentrations of nitrogen, carbon and metals (Al, Co, Cr, Cu, Mn, Ni, Pb and Zn) of the wastewater were measured before, during and after the treatment to assess the effect of the pre-treatment.
Concentrations of nitrogen –mainly ammonium nitrogen- and organic and inorganic carbon appeared to decrease during the pre-treatment, with the larger part of decrease occurring during the aeration step. The decreasing concentration of ammonium nitrogen was mainly explained by the activity of nitrifying bacteria, transforming ammonium into nitrates. The fact that the total nitrogen concentrations decreased, too, suggests other processes and sedimentation going on during treatment. Most likely, the decrease of nitrogen was due to denitrification taking place under the anoxic conditions, as well as nitrogen associated with biomass being removed by sedimentation. The consumption of organic carbon by nitrifying and non-nitrifying bacteria and sedimentation are thought to cause the decrease of organic carbon concentration. All measured metal concentrations decreased during aeration and all but manganese concentration decreased further during sedimentation, which was thought to be due to an increasing pH and a concurring decrease in metal solubility. Despite the decrease in concentrations in ammonia- and nitrate-nitrogen, as well as metals, a decrease in toxicity during and after pre-treatment of the waste water was not indicated by results from acute toxicity tests carried out with luminescent bacteria (Vibrio fischeri). Concentrations of ammonium nitrogen, lead and zinc were still too high in comparison to environmental quality standards. The fact that the oxygen concentration took a long time (ca. 35 hours) to increase during aeration indicates that the nitrification process in this experiment had not yet fully been exploited, and that a longer aeration time could further decrease ammonium nitrogen, lead and zinc concentrations. What is more, other studies on the irrigation of short rotation coppice such as willow plantations with wastewater indicate that the water quality of the treated wastewater in this experiment could act as a fertilizer for willow plants.

Popular Abstract

Landfills: a toxic trouble

Landfills, huge amounts of waste buried under the ground. Having grass grown surfaces, their appearance is luring. For underneath, toxic chemicals created from the waste are piling up. And when it rains, they leak out.

The rules for waste dealing are simple. If you can’t recycle or compost it, you burn it. And if that does not work, you burry it. Cover it with a thick layer of soil, a bright green grass field on top and voila: a harmless looking landfill. Yet this world wide used way of dealing with waste is all but free from problems. For the waste inside does not degrade and each rain drop that sinks though the landfill becomes heavily polluted with chemicals of all sorts, the most important ones being ammonium and metals. Yes, the polluted water leaking out of a landfill, ‘leachate’, is indeed a problem . Especially for landfill owners, since they have to take care of it. One of these landfill owners, is the company MERAB in Rönneholm, Skåne.
So what does MERAB do with its leachate? That depends. Up till now, they spray it over the landfill itself, having the sun vaporizing parts of it. But the sun does not always shine. And during rainy days, only the more leachate is created. Sometimes that much, that MERAB has nowhere to go with it. Nowhere, but the nearest river. No real solution, most of us would agree. Luckily, the European Union agrees as well, pressing landfill owners to clean the leachate at its source: the landfill. So MERAB built a treatment system next to its landfill. That this treatment would improve water quality, was fairly sure. How well it would do this, was still a question. What it took to find out, was a simulation of the treatment in the laboratory. Results: both ammonia and the metals tested decreased in concentration. And all that was needed, were air bubbles.
A few tanks and an air pump was all it took to simulate the planned treatment in Rönneholm. First air was blown into the leachate for two days, then it was simply left to settle for another three days. No complicated technique, one would say. Yet not less effective. What was interesting, was what happened with the ammonium. Because ironically, the solution for this toxicant lies in the polluted water itself. Next to all its toxic chemicals the wastewater houses billions of microbes: ammonium eating microbes, called ‘nitrifiers’. All these microscopically small creatures need from us to start feasting on ammonium is oxygen. Binding oxygen atoms to the nitrogen atoms, they turn toxic ammonium into much less toxic nitrates, a process called ‘nitrification’.
But nitrification is not enough. Although not nearly as toxic as ammonium, nitrates can still cause problems. For they serve as food for mostly algaes and too much food means too much algae. Pumping nitrified leachate into lakes and rivers can increase algaes, which suffocate all other living creatures in that area. Therefore, aeration was stopped after two days. Without oxygen, no nitrates are created. Instead, another group of microbes called ‘denitrifiers’ turn the nitrates into nitrogen gas. These gas bubbles simply rise up to the surface and vanish into the open air.
So all that is needed for leachate treatment is an air pump and patience? Yes and no. Indeed, nitrogen and metals are removed by microbes when there is plenty of oxygen. But the composition of leachate is complex. Organic pollutants, heavy metals and excessive amounts of carbon and nitrogen make only up a small part of the chemical collection found in leachate. And the composition changes over time due to microbial processes in the landfill. They change the landfill content and with that they change the leachate that comes out. Seeing to what ends up in a landfill might therefore offer more control. After all, what goes in decides what comes out. In Sweden, the landfilling of organic material is for example not allowed. This prevents organic pollutants in the leachate, which are difficult to treat and known for their extreme toxicity. In other words, it is better to prevent than to cure. But when this is not possible the microbes fortunately help out.

Supervisor: Martijn van Praagh
Master´s Degree Project in Ecotoxicology 2013, 30 ECTS
Department of Biology, Lund University
Applied project at SWECO

• author: Buijtenhuijs, Daan
• supervisor: Martijn van Praagh
• organization: Degree Projects in Biology
• course: BIOM14 20132
• year: 2014
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 4580934
• date added to LUP: 2014-07-31 11:14:20
• date last changed: 2014-07-31 11:14:20