Building on a series of technical articles written by AFECO specifically for Superyacht Technology magazine on marine wastewater treatment, the latest edit written by the AFECO technical experts explains the importance of alkalinity in biological wastewater treatment.
In the operation and smooth running of a biological sewage treatment plant (STP) one of the parameters which is most often overlooked is alkalinity. Our article looks at what alkalinity is, why it is especially important for on board systems, and what can be done to ensure that everything works as it should.
Biological systems are very sensitive to the pH of the solution in which they are in. Species such as proteins and enzymes will only work properly within a very narrow range of pH values, and can be very susceptible to any changes in pH. Biological wastewater treatment systems in STPs are no different. The bacteria and enzymes which treat the wastewater are also sensitive to pH, and operate most efficiently within the pH range 6.8 to 8.0. The biological wastewater treatment process also generates hydrogen ions, and so alkalinity is needed to keep the pH of the solution in the required range. If the alkalinity is too low then the extra hydrogen ions are not removed, the pH drops, and the speed of the wastewater treatment slows or even stops. If the STP is nitrifying too (converting the ammonia in the wastewater into nitrates) then this process will also consume alkalinity.
This makes it even more complicated, as not only is it does the user need to know the alkalinity of the wastewater prior to treatment, it is also helpful to measure the residual alkalinity of the treated wastewater. The leftover alkalinity is a useful measure of whether the STP’s biological processes are working efficiently.
Alkalinity in natural water comes from the soil and rocks, which the water passes through prior to treatment. This means that the alkalinity present in shore water will vary depending on the geology of where the shore water was treated. It also means that when a vessel changes from shore water to water produced on board (through reverse osmosis), the process will remove the majority of the alkalinity from the water. This has a dramatic effect on the pH, and therefore the performance, of the STP.
As any discharges from a superyacht must comply with MEPC.227(64), this process could also mean owners are breaking the law if not aware of its effects. MEPC.227(64) states that ‘The pH of the samples of effluent taken during the test period should be between 6 and 8.5.” Ensuring an adequate alkalinity concentration in the wastewater will enable the pH to be kept within this range, and so will keep any discharges compliant with the legislation.
The full article can be read here:
AFECO is a dynamic, specialist engineering services and solutions provider focussed on servicing the immediate and future needs of the water, marine and energy sectors. AFECO offer a comprehensive range of professional services, solutions and products, based on a strong core expertise of process, chemical, mechanical, electrical and ICA engineering. With services ranging from the provision of expert consultancy, asset optimisation, concept development, engineering design, site installation and commissioning, AFECO have the skills and experience to provide a complete and integrated project delivery and support service. With a strong focus on robust and appropriate, yet innovative and cost-effective solutions, AFECO have established a reputation of professionalism, efficiency and innovation. AFECO is a subsidiary of EcoGenR8 Limited, a cleantech innovation and development company.
SUPERYACHT TECHNOLOGY is a company dedicated to digital marketing for the superyacht sector and is the only publication focused purely on technology. Through their website and a monthly online interactive magazine, Superyacht Technology seeks to bring the latest technologies to engineers and captains, shipyards, project managers, technical managers and ETO’s.