118
4 Nitrogen and Phosphorous Recovery from Municipal Wastewater …
The Seaborne technology is a combination of different methods such as incineration, acid treatment, desulfurization, methane production, heavy metals separation and struvite precipitation [13]. In this process, an acid solution is added to the
dewatered sludge from anaerobic digestion to lower the pH and dissolve the metals
and nutrients. In the next step, the organic residuals are separated from the soluble
compounds using a centrifuge and the organics are incinerated. The metals in the
soluble fraction are precipitated using hydrogen sulfide from the anaerobic digester.
Metals are then separated by filtration and are treated with sodium hydroxide and
magnesium oxide to precipitate phosphorous in the form of struvite. The advantages
of this technology are the recovery of multiple nutrients with almost no heavy metals
and organic impurities as well as production of biogas free of H 2 S [13].
The BioCon process was developed to recover phosphorous from sludge incineration ash using sulfuric acid. The acid solution is then treated in ion exchange columns
to yield products such as ferric chloride (FeCl 3 ), potassium bisulfate (KHSO 4 ) and
phosphoric acid (H 3 PO 3 ) [13]. Another process for recovery of phosphorous from
sludge incineration ash is the SEPHOS (SEquential precipitation of PHOSphorus)
process. In this method, sulfuric acid is added to the ash to adjust the pH value to
around 1.5. The solid and liquid phase are then separated and the pH of the liquid
phase is again adjusted to around 3.5 in order to precipitate the available phosphorous
and aluminum as AlPO 4 . A caustic solution is added in the second stage to dissolve
the recovered AlPO 4 at high pH values of 12–14 and the dissolved phosphorous is
finally precipitated as calcium phosphate by lime addition [13].
4.4.2 Nitrogen Removal/Recovery from Sludge
Nitrogen recovery from sludge should be performed prior to incineration, often
during the thermal drying of the sludge, as the nitrogen in the sludge would be
released into the environment in the form of flue gas from the incineration process
[47]. The technology for nitrogen recovery from sludge is known as ARP (Ammonia
Recovery Process), developed by the Battelle Memorial Institute in the USA. This
technology is a reversible chemo-sorption process and it was initially developed to
remove nitrogen from the nitrogen-rich effluent of the Sludge-to-Oil Reactor Systems
(STORS). The ARP process concentrates the ammonia in the effluent from around
1000 ppm to 15,000 ppm using an ion exchange unit. The ammonia-rich stream is then
vaporized and the ammonia gas is crystallized as ammonium sulfate by contacting
with sulfuric acid [13].
4.5 Nutrient Recovery Technologies Across the World
Over the past few decades, wastewater has evolved from a waste to be treated to a
renewable resource for energy and resource recovery, resulting in lower fossil energy
4 Nitrogen and Phosphorous Recovery from Municipal Wastewater …
The Seaborne technology is a combination of different methods such as incineration, acid treatment, desulfurization, methane production, heavy metals separation and struvite precipitation [13]. In this process, an acid solution is added to the
dewatered sludge from anaerobic digestion to lower the pH and dissolve the metals
and nutrients. In the next step, the organic residuals are separated from the soluble
compounds using a centrifuge and the organics are incinerated. The metals in the
soluble fraction are precipitated using hydrogen sulfide from the anaerobic digester.
Metals are then separated by filtration and are treated with sodium hydroxide and
magnesium oxide to precipitate phosphorous in the form of struvite. The advantages
of this technology are the recovery of multiple nutrients with almost no heavy metals
and organic impurities as well as production of biogas free of H 2 S [13].
The BioCon process was developed to recover phosphorous from sludge incineration ash using sulfuric acid. The acid solution is then treated in ion exchange columns
to yield products such as ferric chloride (FeCl 3 ), potassium bisulfate (KHSO 4 ) and
phosphoric acid (H 3 PO 3 ) [13]. Another process for recovery of phosphorous from
sludge incineration ash is the SEPHOS (SEquential precipitation of PHOSphorus)
process. In this method, sulfuric acid is added to the ash to adjust the pH value to
around 1.5. The solid and liquid phase are then separated and the pH of the liquid
phase is again adjusted to around 3.5 in order to precipitate the available phosphorous
and aluminum as AlPO 4 . A caustic solution is added in the second stage to dissolve
the recovered AlPO 4 at high pH values of 12–14 and the dissolved phosphorous is
finally precipitated as calcium phosphate by lime addition [13].
4.4.2 Nitrogen Removal/Recovery from Sludge
Nitrogen recovery from sludge should be performed prior to incineration, often
during the thermal drying of the sludge, as the nitrogen in the sludge would be
released into the environment in the form of flue gas from the incineration process
[47]. The technology for nitrogen recovery from sludge is known as ARP (Ammonia
Recovery Process), developed by the Battelle Memorial Institute in the USA. This
technology is a reversible chemo-sorption process and it was initially developed to
remove nitrogen from the nitrogen-rich effluent of the Sludge-to-Oil Reactor Systems
(STORS). The ARP process concentrates the ammonia in the effluent from around
1000 ppm to 15,000 ppm using an ion exchange unit. The ammonia-rich stream is then
vaporized and the ammonia gas is crystallized as ammonium sulfate by contacting
with sulfuric acid [13].
4.5 Nutrient Recovery Technologies Across the World
Over the past few decades, wastewater has evolved from a waste to be treated to a
renewable resource for energy and resource recovery, resulting in lower fossil energy