Struvite production from anaerobic digestate of piggery wastewater using ferronickel slag as a magnesium source

ABSTRACT

This study aimed to fully recover ammonia contained at a high concentration in anaerobic digestate of piggery wastewater (ADPW) by forming struvite. As magnesium and phosphorus sources, ferronickel slag (FNS) and K₂HPO₄ were used, respectively. By leaching 200 g L⁻¹ of FNS with 3.0 M H₂SO₄, 10,309 mg L⁻¹ of magnesium ions were extracted, and this acid-leachate of FNS (FNSL) also contained 5965 mg L⁻¹ of total iron. In order to simultaneously remove both high concentrations of organic matters in ADPW and iron in FNSL which were known to hinder struvite formation, the mixture of ADPW and FNSL was added with H₂O₂ at the H₂O₂/Fe molar ratio of 0.75 and pH 4.0. After Fenton reaction, removal efficiencies of COD and total iron reached 77.36% and 99.89%, respectively. Then COD and an iron-reduced mixture of ADPW and FNSL were added with K₂HPO₄ satisfying Mg:N:P molar ratio of 1.2:1:1.15 at pH 9.5 to produce struvite for 1 h. From 1 L of ADPW (2.21 g NH₃-N), 0.65 L of FNSL (4.65 g Mg²⁺), and 5.63 g of PO₄^3–P, 46.7 g of precipitates were obtained. Overall removal efficiencies of magnesium, NH₃-N, and phosphorus were 98.59%, 94.25%, and 99.97%, respectively. Obtained precipitates were analysed by using XRD, XRF, SEM-EDX and found to be struvite with impurities of potassium and metals. Additionally, the economic feasibility of FNS was assessed by estimating chemical costs of various magnesium sources.

GRAPHICAL ABSTRACT

KEYWORDS:

• Acid extraction
• anaerobic digestate of piggery wastewater
• Fenton reaction
• ferronickel slag
• struvite

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Gyutae Kwon http://orcid.org/0000-0003-1474-5487

Jinyoung Kang http://orcid.org/0000-0003-3265-7712

Ji-Hyun Nam http://orcid.org/0000-0001-7623-5015

Young-O. Kim http://orcid.org/0000-0001-6379-0597

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This study was supported by the R&D Centre for Organic Wastes to Energy Business (under the Wastes to Energy Technology Development Program) funded by the Ministry of Environment, Republic of the Korea (Project No. 2013001580002). This work was supported by NRF (National Research Foundation of Korea) Grant funded by the Korean Government (NRF-2018011304-Global Ph. D. Fellowship Program)