Potentials of using nanofiltration to recover phosphorus from sewage sludge

Abstract

Due to the depletion of mineral phosphorus resources there is an increasing demand for efficient phosphorus recovery technologies. In this study the potential of nanofiltration to recover phosphorus from pre-treated sewage sludge is investigated. The efficiency of three commercial nanofiltration membranes (Desal 5DK, NP030; MPF34) was tested using model solutions. Desal 5DK showed the best selectivity for phosphorus. A pH of lower than 1.5 was found to be most suitable. Desal 5DK was used on four different sewage sludge ash eluates and on one sewage sludge. In these experiments it was shown that a separation of phosphorus from undesired components such as heavy metals was possible with significant variations in the efficiency for the different ash and sludge types. Additionally the achievable product recovery was investigated with model solutions. A product recovery of 57.1% was attained for pH 1 and 41.4% for pH 1.5.

Phosphorus recovery from sewage sludge by nanofiltration in diafiltration mode

“…As a consequence, nanofiltration membranes are not only size-selective, but also ion-selective and their performance depends heavily on the pH of operation [9,10]. If the dissolution of sewage sludge is done by acidic dissolution, the feed stream for the filtration step has a pH value around 1.5 [7,11]. Under these conditions, nanofiltration membranes exhibit a strong positive surface charge and phosphorus is mainly present in the form of undissociated or only mono-dissociated phosphoric acid.…”

“…Some research focused particularly on nanofiltration for the recovery of phosphorus from sewage sludge and sewage sludge ash [11,14,15]. Based on these studies, a nanofiltration process with a high phosphorus yield in the permeate was developed in this work.…”

Assessment of Layer-By-Layer Modified Nanofiltration Membrane Stability in Phosphoric Acid

“…The application of NF for spent pickling acid and pickling baths, especially H 3 PO 4 , is still an emerging technology [3,8]. The applicability of NF was shown for P recovery from sewage sludge [9][10][11]. P concentrations in the acidified sewage sludge ash are much lower than in pickling acids.…”

“…In the studies by Schütte et al or Niewersch, commercially available membranes were used to retain metals and heavy metals but allow the permeation of P in the form of H 3 PO 4 . The concept was proven to be successful, yet the process is not economically feasible due to high P retention and low fluxes [9][10][11]. Schütte et al concluded that for the recovery of metal contaminated H 3 PO 4 solutions, a highly permeable membrane with a low retention for H 3 PO 4 and highly positively charged ion retention is favourable.…”

Technical and economical assessment of formic acid to recycle phosphorus from pig slurry by a combined acidification–precipitation process

“…The mineral product obtained by precipitation of phosphorus from the enriched supernatant can then be used for agricultural purposes. This technique has been already been tested in previous studies on pig slurry [9], poultry litter [10] and ashes [11]. Because of the acidic pH of the supernatant, the solubility of the reactant is increased and magnesium oxide or hydrated lime can easily be used to increase the pH and to simultaneously supply cations.…”