4.5 Nutrient Recovery Technologies Across the World
121
the operations prevent the onsite application of many nutrient removal technologies
developed to wastewater treatment plants [52].
4.6 Economic Analysis of Nutrient Recovery
from Municipal Wastewater and Sludge
Nitrogen and phosphorous are the two main nutrients required for crop growth.
Nitrogen-based fertilizers can be produced from atmospheric nitrogen sources using
Haber–Bosch process at a low cost. The low price for nitrogenous fertilizer production is a great barrier for the economic viability of the nitrogen recovery from wastewater or sludge. However, phosphorous is mined from mineral reserves that are relatively limited. Thus, there is a greater motivation for phosphorous recovery compared
to nitrogen.
Mining phosphorous is associated with environmental impacts such as habitat
destruction at mine sites, emissions to the air from refining processes and carbon
footprints. Nutrient recovery from wastewater and sludge is able to eliminate the
economical and environmental impacts of fertilizers production. For example, using
phosphorous recovered from waste streams avoids these impacts and provide more
environmentally friendly solutions to fertilizer production [53].
Nutrient recovery has the benefits of providing supplementary fertilizers for food
production as well as offsetting wastewater treatment costs. The nutrient recovery
from the wastewater (liquid phase) is cheaper than that from the sludge phase as
the nutrients in the sludge need additional treatments to make them accessible in
the solution for recovery. Moreover, the recovery of nutrients from the sludge may
result in production of unexpected by-products such as heavy metals which requires
additional disposal [29].
In the case of chemical precipitation processes for phosphorous recovery, the
chemicals used for increasing pH and the energy used for mixing form the major
proportion of the total cost. Since most of the wastewaters are slightly acidic, a
lot of alkali is required to increase pH, which contributes to more than 90% of
the operational cost. Aeration through CO 2 stripping could be an alternative and
more economical solution for pH elevation. When chemical precipitation is used for
nutrient recovery in coastal areas, seawater could be used as a low-cost source with
high magnesium content for chemical precipitation. In thermochemical treatments,
using a heat exchanger reduces the energy consumption while the methane gas generated onsite from anaerobic digestion could be used as a supplementary energy source.
Renewable energy such as solar energy could also be used as a supplementary energy
source for nutrient recovery to reduce the energy costs and enhance the economic
feasibility of the process [29].
121
the operations prevent the onsite application of many nutrient removal technologies
developed to wastewater treatment plants [52].
4.6 Economic Analysis of Nutrient Recovery
from Municipal Wastewater and Sludge
Nitrogen and phosphorous are the two main nutrients required for crop growth.
Nitrogen-based fertilizers can be produced from atmospheric nitrogen sources using
Haber–Bosch process at a low cost. The low price for nitrogenous fertilizer production is a great barrier for the economic viability of the nitrogen recovery from wastewater or sludge. However, phosphorous is mined from mineral reserves that are relatively limited. Thus, there is a greater motivation for phosphorous recovery compared
to nitrogen.
Mining phosphorous is associated with environmental impacts such as habitat
destruction at mine sites, emissions to the air from refining processes and carbon
footprints. Nutrient recovery from wastewater and sludge is able to eliminate the
economical and environmental impacts of fertilizers production. For example, using
phosphorous recovered from waste streams avoids these impacts and provide more
environmentally friendly solutions to fertilizer production [53].
Nutrient recovery has the benefits of providing supplementary fertilizers for food
production as well as offsetting wastewater treatment costs. The nutrient recovery
from the wastewater (liquid phase) is cheaper than that from the sludge phase as
the nutrients in the sludge need additional treatments to make them accessible in
the solution for recovery. Moreover, the recovery of nutrients from the sludge may
result in production of unexpected by-products such as heavy metals which requires
additional disposal [29].
In the case of chemical precipitation processes for phosphorous recovery, the
chemicals used for increasing pH and the energy used for mixing form the major
proportion of the total cost. Since most of the wastewaters are slightly acidic, a
lot of alkali is required to increase pH, which contributes to more than 90% of
the operational cost. Aeration through CO 2 stripping could be an alternative and
more economical solution for pH elevation. When chemical precipitation is used for
nutrient recovery in coastal areas, seawater could be used as a low-cost source with
high magnesium content for chemical precipitation. In thermochemical treatments,
using a heat exchanger reduces the energy consumption while the methane gas generated onsite from anaerobic digestion could be used as a supplementary energy source.
Renewable energy such as solar energy could also be used as a supplementary energy
source for nutrient recovery to reduce the energy costs and enhance the economic
feasibility of the process [29].