This beaker includes the effluent from the settling thickening tank. Do you think that this effluent is safe for discharging to water body? Or for use for irrigation agriculture? What if I tell you that this has higher concentrations of organics and nutrients, than waste water. And that the salt concentrations could be harmful to plants. In this module, I'll introduce you to treatment technologies to treat such an effluent. Following this module, you'll be able to name potential difference between effluents from treatment technologies and compared to waste water. You will also be able to name potential effluent treatment technologies and discuss potential challenges with effluent treatment. Because of high concentration faecal sludge of solids and organics, solid liquid separation technologies are often the first treatment technology at a treatment plant. Followed by further separate treatment of the solids and the liquid effluent. This liquid effluent is also called leachate or percolate or supernatant This table shows values from the literature for suspended solids Chemical Oxygen demand, also called COD, Ammonium Nitrogen in the liquid effluent from unplanted drying beds Planted drying beds and in comparison to domestic waste water and common discharge standards. There are three main messages that you should take away from this table. Firstly, the effluent concentration can be very different depending on the treatment technology. For example, based on this values unplanted drying beds were higher in COD and Ammonium Nitrogen than planted drying beds. This means that concentration in liquid effluents from different solid liquid separation technologies need to be taken into account for design of effluent treatment technologies. Secondly, Effluent concentrations do not meet common discharge requirements for suspended solids, COD, and Ammonium Nitrogen. And further treatment is required to protect environmental health. Liquid effluents also commonly have high salt concentrations, they can can harmful to plants, and contain pathogens that require inactivation before discharge. Thirdly, even after solid liquid separation these effluents can have much higher concentrations than the influent of a domestic wastewater treatment plant. For example, whereas suspended solids concentrations in the leachates from drying beds are somehow similar to domestic waste water. COD and ammonium concentrations can be one order of magnitude higher. Technologies that are used to treat effluents from the solid liquid separation technologies include different types of waste stabilisation ponds, constructed wetlands, planted drying beds, anaerobic baffled reactors and anaerobic filters. Let's have a look at two examples of currently operating effluent treatment configurations at faecal sludge treatment plants. One in the Philippines and another one in India. This picture shows the feacal sludge treatment plant in Dumaguete, the Philippines that is introduced in another module. Dumaguete has a treatment capacity of 80 cubical faecal sludge, which is mainly collected from septic tanks by vacuum trucks. Following discharge through a screen, solids and liquids are separated in anaerobic waste stabilization ponds. Solids are then being dewatered on drying beds. The treatment chain for the liquid effluent from the anaerobic waste stabilization ponds include one facultative pond, two maturation ponds in series and then a constructed wetland prior to discharge. Waste stabilization ponds also called lagoons treat effluents in large engineered lined basins. Facultative ponds that are used at Dumaguete following solid liquid separation have a depth of 1 to 2.5 meters and are designed for removal of dissolved and suspended organics. They are called facultative ponds because they are stratified into a top level which is predominantly aerobic. and a bottom layer which is predominantly anaerobic, so has no Oxygen At Dumaguete maturation ponds follow these facultative ponds. Maturation ponds usually have a depth of 0.5 to 1.5 meters. Are aerobic and are designed for inactivation of pathogens. The hydraulic retention time of these ponds is usually several days to weeks. Which explains why they are land intensive and require a lot of space. At Dumaguete the effluent from the maturation ponds is further treated in constructed wetlands as shown behind me. This slide shows the schematic of a constructed wetland. Which is also called planted gravel filters and is very similar to a planted drying bed in its design and operation. Constructed wetlands are basins filled with gravel and sand with plants that can grow in these conditions such as antelope grass or Echinochloa pyramidalis. Constructed wetlands can be distinguished and operated as horizontal flow, so when the effluent flows from one end to the other end horizontally. Or vertical flow, where it flows from the top to the bottom. Similar to a planted drying bed. During its passage, suspended and dissolved organics are separated by filtration and removed from the liquid effluent by microorganisms attached to the filter media and the plant roots. The purpose of thes plants is to ensure permeability of the filter media, provide surface for growth of microorganisms and take up nutrients. Efficient solid liquid separation is required before the use of constructed wetlands to prevent clogging of the filter media. This picture shows a research facility of Sandec at the university of Yaounde in Cameroon. Here a series of planted drying beds was able to reduce concentration organics and nutrients by 80%. You can download a publication of this research for free from our website. This picture shows the faecal sludge treatment plant in Devanahalli north of Bangalore in India. In contrast to Dumaguete, Devanahalli only has a treatment capacity of 6 cubic meters per day and receives mostly sludge from pit latrines. This is one reason why different treatment technologies were selected for the effluent treatment. Following discharge through a screen solids and liquid are separated by a settling tank. Following solid liquid separation, the solids are treated in parallel by anaerobic digesters. Followed by another settling tank after which solids are dewatered on unplanted drying beds. Instead of waste stabilization ponds used at Dumaguete the liquid effluent from the settling tanks is treated in an anaerobic baffled reactor which is also called ABR followed by a treatment in constructed wetlands. This slide shows a schematic of an anaerobic baffled reactor as used in Devanahalli. They are concrete or plastic tanks with a series of baffles. In the schematic they are 5. They're designed for removal of organics. The baffles force the effluent to flow down into next chamber and up through a sludge layer. This can increase the performance of the removal of organics. For example, in comparison to a septic tank. We have now introduced you to some treatment technologies for the liquid effluent from solid liquid separation technologies. If you would like to learn more about these technologies, you could have a look at these three publications developed for waste water. They can be downloaded for free from these websites. Currently, the design of the technologies discussed in this module, are based on existing technologies, that need to be adapted for effluents from solid liquid separation of faecal sludge. This could carry certain risk for reliable treatment that you should consider. For example, organics in faecal sludge may already be partially digested, which could reduce the effectiveness of anaerobic treatment technologies. Such as anaerobic baffled reactors discussed before. This is likely due to long storage duration in onsite sanitation technologies. As discussed at the beginning of this module, faecal sludge can have high Ammonium concentrations. As a function of pH and temperatures this means that faecal sludge can have high Ammonia concentrations that can be toxic for bacteria and algae and inhibit treatment processes, for example, in facultative ponds or anaerobic baffled reactors. With smaller faecal sludge treatment plants as the one shown in Devanahalli, India, hydraulic shock loads, for example, by a discharge of one big vacuum truck can also be a challenge because it can flush out the sludge and microorganisms that are valuable for treatment. Variable treatment characteristics, for example, from septic tanks versus the pit latrine are also challenging for such technologies. In this module, we discussed that treatment plants can produce several liquids that require further treatment. In general, these liquids have high concentration of organics nutrients and salinity, which are often higher than in waste water. As shown for two treatment plants, one in the Philippines and another one in India, waste stabilization ponds, constructed wetlands, and anaerobic baffled reactors are among the treatment technologies used for effluent treatment. A low fraction of biodegradable organics, high Ammonia concentration or hydraulic shock loads can be challenges with effluent treatment and should be considered.
