Optimizing the H3PO4 leaching conditions of post-precipitated sewage sludge using response surface methodology
The leaching procedure of post-precipitated aluminium phosphate sludge with dilute phosphoric acid was developed. The leaching offers a route to recover both critical phosphorous from sewage sludge and the metal used in precipitation. Using phosphoric acid as leaching solution makes it possible to continue the recovery process without the need to remove chloride or sulfate anions. The optimization of the leaching was based on experimental three-level-four-variable central composite face-centered design. The four variables included were acid concentration, volume of acid, temperature and time of leaching. The leaching was conducted for dewatered and water-containing sludge (total solid conte…
Fosforin jälkisaostus ja saostuskemikaalin kierrätys
Tämän pro gradu -tutkielman kirjallisessa osiossa perehdyttiin fosforin saostamiseen vaikuttaviin tekijöihin ja mahdollisiin menetelmiin jatkokäsitellä puhdistetusta jätevedestä saostettua fosforisaostumaa, siten että saostuskemikaalin metalli olisi uudelleen käytettävissä ja fosfori teollisuudelle ja kasveille käyttökelpoisessa muodossa. Mahdol-lisiksi menetelmiksi jatkokäsittelyyn valikoituivat ioninvaihto ja kalsiumsaostus. Kokeellisessa osiossa fosforin saostamista puhdistetusta jätevedestä testattiin kolmella eri saostuskemikaalilla ja niistä saatujen saostumien liukenevuutta kokeiltiin eri happoihin ja emäksiin. Tämän lisäksi tutkittiin ioninvaihdon ja kalsiumsaostuksen toimivuutta sa…
RAVITA Technology : new innovation for combined phosphorus and nitrogen recovery
Abstract Present phosphorus (P) recovery technologies mainly contain P recovery from sludge liquor or ash. These types of technologies are suitable for large wastewater treatment plants (WWTPs) with enhanced biological phosphorus removal (EBPR), digestion and/or incineration. In Finland and other Nordic countries, strict P discharge limits require chemical precipitation, thus EBPR alone is not sufficient. Ammonium recovery from wastewater, on the other hand, is not so often discussed. However, recovery from WWTP reject waters would decrease the energy demand of ammonium synthesis by Haber-Bosh technology and the energy demand of the WWTP's biological process. Helsinki Region Environmental S…
To incinerate or not? - Effects of incineration on the concentrations of heavy metals and leaching efficiency of post-precipitated sewage sludge (RAVITA™).
The major element and heavy metal concentrations of post-precipitated sewage sludge (PPS) and its ash residue (PPA) were determined using microwave digestion followed by inductively coupled plasma optical emission spectrometry (ICP-OES) and mass spectrometry (ICP-MS). To the best of our knowledge, this has not been previously done. In both PPS and PPA the heavy metal concentrations were clearly below the average concentrations than those encountered in sewage sludge in Europe. The leaching efficiency of the metal (Al/ Fe) used as a precipitation agent from post-precipitated sludge and its ash residue with phosphoric acid was also investigated with previously optimized leaching conditions. T…
Purification of recovered phosphoric acid by extracting aluminium with di-2-ethylhexyl phosphoric acid
AbstractThe extraction of aluminium from dilute phosphoric acid with di-2-ethylhexyl phosphoric acid (DEHPA) was optimized using response surface methodology. The optimization was based on the experimental three-level central composite face-centred design (CCF) and was conducted on real-life samples. The three variables included were pH, extractant concentration and aqueous to organic phase ratio (AO). Under the optimized conditions (pH 2.5, 0.6 M DEHPA and AO ratio 1:2), extraction efficiency of 99% for aluminium in four extraction stages is achieved. The purified phosphoric acid solution can then be utilized by the fertilizing industry. Stripping tests for organic phase loaded with alumin…