Water Treatment Plant Improvements
A WWTP is a wastewater treatment plant, that is, a chemical plant in which water-based effluents from industrial activity or domestic consumption are treated, in order to reduce their level of contamination to the point of being able to be discharged into a receiving channel, such as a river, a sea or a reservoir. At the moment, it is essential to know what improvements of sewage plants can be implemented so that they are more efficient and safer.
One of the trends is to increase economic performance through the use of biogas—composed of 50% to 70% of methane—resulting from the stages of treatment of effluents or sludge with anaerobic microorganisms. Some solid by-products from wastewater treatment plants are composted, to be reused instead of being stored in specialized plants.
There are physical-chemical, biological, most common, and mixed wastewater treatment plants. The physical-chemical WWTPs involve large costs for the installation.
The improvements of wastewater treatment plants may seek to increase the effluent flow that it is capable of processing, to improve the energy efficiency of one or several stages of the process, or to replace the machinery of one or more stages with more modern equipment, which require less space or allow a higher level of purification with the same energy cost.
If a wastewater treatment plant should increase the effluent flow that it treats continuously, it is very possible that a lot of equipment will need to be changed, such as the endless screw, or to establish parallel work lines when it is not possible. In any case, it is an improvement that requires large investments and available land around the plant.
As explained, improvements to treatment plants may seek to use equipment of smaller dimensions or other that offer a higher level of purification, allowing shorter processing times.
The replacement of equipment that is ending its useful life with others that occupy a smaller area may allow a WWTP to add additional stages in case of not having more land for it. These additional stages usually seek to increase the energy and economic yields of what the purification of the wastewater flow usually treated is, analyzing the process in a global way.
We talk of usual work flow to differentiate it from increases due to natural causes, such as floods, for which the plant must be prepared thanks to the oversize in the design of each unit stage. Economic balances are made considering normal working conditions.
Improvements in the energy efficiency of the purification process are done in two ways. On the one hand, when the useful life of a device, such as a decanter or a centrifugal pump, is being terminated, the new options offered by industrial equipment suppliers will be assessed, making an economic balance that determines whether something new is amortizable or not.
In general, the WWTPs are designed so that their equipment has a useful life of 8–10 years, except for unforeseen breakdowns, and it is estimated that the investments should be amortized before six years.
But the economic performance of a sewage treatment plant also improves when the plant’s energy consumption is reduced. For this, it is usual to add one or two additional stages to the global process, in order to take advantage of the generated biogas and some other by-product, which could become the raw material of another plant or be sold.
As we have explained, in reality, one of the improvements of wastewater treatment plants that are being implemented most in Spain and that includes all recently created WWTPs is the stage of biogas use through a combustion process, with the aim of producing energy to supply the facilities. However, we must not forget that this improvement is still not enough to make these plants completely self-sustaining from an energy point of view.