Effective Nitrogen Removal and Recovery from Dewatered Sewage Sludge Using a Novel Integrated System of Accelerated Hydrothermal Deamination and Air Stripping

Abstract

In order to reduce considerable emissions of Ncontaining pollutants from combustion of sewage sludge derived solid fuel, an integrated system of hydrothermal deamination and air stripping was developed to effectively remove and recover nitrogen from dewatered sewage sludge (DSS). Three characteristic hydrothermal regimes contributing to deamination were identified. Initial hydrolysis of inorganic-N and labile protein-N was responsible for ammonium (NH 4 + -N) released below 300 °C/9.3 MPa, whereas deamination of pyridine-N dominated when being raised to 340 °C/15.5 MPa. At 380 °C and 22.0 MPa, remarkable deamination of stable protein-N occurred, which was accompanied by formation of more heterocyclic-N compounds and resulted in 76.9% N removal from DSS and 7980 mg/L NH 4 + -N solution. As a result of catalytic hydrolysis and cracking, calcium oxide additive not only accelerated deamination of stable protein-N, pyrrole-N, and pyridine-N, but also favored transformations of protein-N and quaternary-N to nitrile-N and pyridine-N, respectively, leading to 86.4% total N removal efficiency. The nitrogen transformation reactions and conversion pathways during hydrothermal deamination were proposed and elaborated in detail. Moreover, an efficient air stripping process was coupled to remove and recover ammonia from liquid fraction via ammonium sulfate. Consequently, this system achieved an overall N recovery rate of 62%.

Process Waters from Hydrothermal Carbonization of Sludge: Characteristics and Possible Valorization Pathways

“…The same authors showed that even if a high moisture content could favor hydrolysis, increasing the moisture content of the initial digestate, the dilution effect dominates the nitrogen evolution in the process waters, thus reducing the concentration of total dissolved nitrogen and ammonia. He et al [ 83 ] confirmed the catalysis role of CaO in promoting hydrolysis or cracking of N-containing compounds, as both NH 4 + -N and organic N increased substantially in process waters. Additionally, as the Ca/C molar ratio was raised from 0.05 to 0.2, NH 4 + -N further increased, reaching the 83% of total nitrogen in process waters, while organic N decreased.…”

“…The effect of calcium oxide on the evolution profile and characteristics of gas, solid and liquid by-products of HTC from ADSS was reported by He et al [ 59 ]. The phosphorous and heavy metal distribution in the by-products of dewatered ADSS was investigated by several authors [ 83 , 84 ]. In order to reduce the considerable emissions of N-containing pollutants from combustion of the sewage sludge-derived solid fuel, an integrated system of hydrothermal deamination and air stripping from HTC water processing was developed to effectively remove and recover nitrogen from dewatered sewage sludge [ 59 ].…”

“…Depending on the feedstock, HTC at different temperatures affects the distribution of nitrogen in HTC by-products, as a result of hydrolysis of proteins and the ammonium release. N-containing compounds are mainly present in HTC solid and liquid by-products, while N-containing gas is negligible [ 83 ]. He et al [ 28 ] found that after HTC treatment of dewatered ADSS, N tended to release into process waters: 40% of N remained in the hydrochar while almost 60% was released into liquid phase.…”

Structured Approach for Comparison of Treatment Options for Nutrient-Recovery From Fecal Sludge

“…Incineration and carbonization technologies failed to meet the prerequisite for macro nutrient recovery since these treatments fully eliminate nitrogen and sulfur. It is noted that hydrothermal carbonization can retain ∼30-60% of the nitrogen in the hydrochar, depending on process temperature and feedstock (He et al, 2015;Wang et al, 2018). However, the high temperatures, high pressure and complex processing needed for this technology are not deemed feasible at Lubigi.…”

Recovery of nutrients from wastewater by a MgCl2 modified zeolite and their reuse as an amendment for Cu and Pb immobilization in soil

“…(2) To investigate the effect of dosage of modied zeolite, contact time and pH on AN and phosphate removal, and obtain the optimal parameters of nutrients removal by magnesium modied zeolite. (3) To apply recovery materials collected under optimal condition for heavy metal immobilization in contaminated soil.…”