Recovery of nutrients from digested sludge as struvite with a combination process of acid hydrolysis and Donnan dialysis

Abstract

In this study, the effects of the combination of acid hydrolysis and Donnan dialysis on the high-quality struvite production from digested sewage sludge were examined. The Box-Behnken design was applied in the hydrolysis using oxalic acid for the optimization of the conditions that affect the nutrients and metal release from digested sludge. An optimal condition was obtained at oxalic acid 0.5 M, acid/sludge ratio (mL/g) 10/1, and reaction time 60 min. The separation of the metals from hydrolyzed sludge liquid was carried out with the Donnan dialysis using a Nafion 117 cation exchange membrane. At the end of the 4 hours of operating time, the recovery values for Zn, K, Na, Mg, Fe, and Al were obtained as 67.9%, 62.1%, 57.6%, 39.4%, 5.3%, and 2.5%, respectively. The produced struvite meets the legal limits for fertilizer use in terms of Cd, Cu, Ni, Pb, Zn, Hg, and Cr content specified by Turkish regulations. A high Ca/Mg molar ratio and the presence of K, Na, and Al affected the efficiency of struvite crystallization. The use of oxalic acid resulted in low Ca release, and the metal ions that affect struvite purity were eliminated using Donnan dialysis.

Agricultural and non-agricultural directions of bio-based sewage sludge valorization by chemical conditioning

“…The recovery of iron, magnesium, aluminium, sodium and potassium was obtained at 5, 39, 3, 58, 62 and 68%, respectively. Hydrolysis with oxalic acid reduced the release of calcium, which negatively affects the purity of struvite, and the use of dialysis eliminated undesirable metal ions (Uysal et al 2017 ). Chen et al ( 2020 ) proposed the hydrolysis of sludge from the municipal sewage treatment plant with oxalic acid.…”

“…Donnan dialysis (DD) is an effective method for the selective separation of heavy metal ions from hydrolysates. The solution obtained by membrane separation meets the requirements for heavy metal limits in fertilizers (Uysal et al 2017). Undoubtedly, the need to remove unwanted components from sludge chemical treatment solutions is a crucial task.…”

“…Despite the benefits, there occurred Cd accumulation in rice grains above acceptable levels (at SS dose of 20t/ha and more) (Latare et al 2014). Uysal et al (2017) proposed the use of sludge from acid hydrolysis for fertilizing. The obtained struvite was purified with Donnan dialysis, which reduced toxic elements to acceptable fertilizer levels.…”

“…Uysal et al ( 2017 ) proposed the use of sludge from acid hydrolysis for fertilizing. The obtained struvite was purified with Donnan dialysis, which reduced toxic elements to acceptable fertilizer levels.…”

Recovery of Nitrogen And Phosphorus In Sewage Sludge by Pulsed Electrical Field Technique and Strüvite Production

“…Bunun yanında doğada ve canlılarda kalıcı özelliğe sahip poliklorlu bifeniller (PCB) gibi organik mikrokirleticiler ve polisiklik aromatik hidrokarbonlar (PAH) gibi aromatik hidrokarbonlar da içerebilmektedirler [3]. Atık çamur yüksek azot ve fosfor içeriğine sahip olmasına rağmen patojen, ağır metal ve diğer kirleticiler nedeniyle gübre olarak tarımsal alanlarda doğrudan kullanılamaz [4]. Arıtma çamurlarının stabilize edilerek toprakta kullanımı mümkündür ve bu konuda yasal düzenlemeler mevcuttur [5].…”