Sewage sludge thermal treatment technologies with a focus on phosphorus recovery: a review

Phosphorus presents a limited, irreplaceable and essential nutrient necessary for the growth of organisms. There is an increasing effort to recover phosphorus from production waste streams. Sewage sludge presents an important source of phosphorus but also contains organic pollutants and heavy metals. Thermal treatment technologies seem to be a promising option to treat sewage sludge and obtain ash/char from which high recovery rate of phosphorus can be reached. In this review, sewage sludge management options in compliance with EU legal requirements are first reviewed. Follows, an overview of sewage sludge thermal treatment technologies including incineration, hydrothermal carbonisation, pyrolysis and gasification, for the purpose of phosphorus recapture. We summarize recent advances in thermal treatment processes of sewage sludge and phosphorus recovery, identify challenges and knowledge gaps. Thermochemical methods proved to have many advantages over pure wet chemical methods for phosphorus recovery. The review provides the foundation for future research aimed at achieving efficient, economic and environmental sustainable recapture of phosphorus from sludge thermal treatment products

Tar from pilot scale co-pyrolysis of biological dairy sludge and spruce wood chips

A pilot scale investigation of co-pyrolysis of biological dairy sludge and spruce wood chips and pyrolysis of spruce wood chips solely was carried out. Pyrolysis was tested as a waste treatment method aiming to reduce the volume of dairy sludge while producing a pyrolysis gas suitable for an internal combustion engine. Pyrolysis tests were carried out in a continuously fed, pilot scale rotating retort type of facility in the temperature range between 700 and 770 °C. Feedstock feeding rates were between 40.9 – 68.6 kgd.a.f. h-1. Tar yields and composition was measured by means of the solid phase adsorption method in order to assess gas quality with regard to the specified tar limits given for downstream applications. The yields of total gas chromatography detectable tar produced from the dairy sludge and spruce wood chips blend was in the range between 7.25 - 10.98 gtotal tar Nm-3 dry raw gas, while spruce wood chips solely produced yields between 11.18 - 13.31 gtotal tar Nm-3 dry raw gas. Composition wise, the main difference was a number of nitrogen-containing tar compounds reflecting the high nitrogen content in dairy sludge feedstock with 2-butenenitrile, pyridine and 1H-pyrrole being the most abundant nitrogen-containing tar compounds. Raw pyrolysis gas from the two feedstocks tested did not meet the requirements regarding tar limits given in the manufacturer’s specification for their internal combustion engine. The raw pyrolysis gas contained excessive amounts of 3 and 4+ aromatic ring tars. Therefore tar removal is required prior to combustion in the engine. The proposed tar removal strategy includes a thermal tar reformer using air as a reforming agent followed by adsorption using wood chips, or in-process generated bio-char, or torrefied biomass as a viable adsorbent

Speciation of Nutrients in Hydrochar Produced from Hydrothermal Carbonization of Poultry Litter under Different Treatment Conditions

In this study, the effects of operating parameters on the behavior of nutrients during hydrothermal carbonization (HTC) of poultry litter (PL) were investigated. A number of HTC experiments were carried out using PL at different treatment temperatures, residence times, and initial pH. The standard measurement and testing protocol was adapted to determine the phosphorus (P) species in the solid hydrochar (HC), while the Ca, K, Mg, Na, Al, Zn, Mn, Fe, Cu, Cr, and Pb contents in each fraction were quantified and related to the P fractions. The results indicate that HTC can effectively reduce the solubility of most of the measured elements. The treatment temperature and initial pH can significantly influence the speciation of P and other nutrients, while the residence time effects were apparent at low treatment temperature. The majority of the measured nutrients remained in the HC when the hydrochar was produced without additional acid. Addition of acids, particularly H₂SO₄, provides a good approach for nutrient recovery

Hydro-pyrolysis and catalytic upgrading of biomass and Its hydroxy residue fast pyrolysis vapors

Fast pyrolysis of Miscanthus, its hydrolysis residue and lignin were carried with a pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) followed by online vapor catalytic upgrading with sulfated ZrO2, sulfated TiO2 and sulfated 60 wt.% ZrO2-TiO2. The most evident influence of the catalyst on the vapor phase composition was observed for aromatic hydrocarbons,light phenols and heavy phenols. A larger amount of light phenols was detected, especially when 60 wt.% ZrO2-TiO2 was present. Thus, a lower average molecular weight and lower viscosity of bio-oil could be obtained with this catalyst. Pyrolysis was also performed at different pressures of hydrogen. The pressure of H2 has a great effect on the overall yield and the composition of biomass vapors. The peak area percentages of both aromatic hydrocarbons and cyclo-alkanes are enhanced with the increasing of H2 pressure. The overall yields are higher with the addition of either H2 or sulfated catalysts. This is beneficial as phenols are valuable chemicals, thus, increasing the value of bio-oil. The results show that the hydrolysis residue has the potential to become a resource for phenol production

A Rapid HPLC method for the simultaneous determination of organic acids and furans: food applications

Concerns over the potential adulteration of commercially produced foods give rise to a requirement for a simple and fast analytical method capable of quantifying potential adulterants. This work demonstrates a simple HPLC method tailored to detect major organic acids and furans within ingredients in commercial food products, for example, pomegranate molasses, balsamic vinegar, and apple cider vinegar. The relative importance of this method is in its simplicity and its use of an environmentally friendly aqueous mobile phase under isocratic conditions, providing results in a less than 20 min runtime. The chromatographic separation was achieved using an Acclaim® OA, 5 µm, 120 Å (4.0 × 250 mm) column; a UV-DAD detector set at 210 nm; and a 200 mM Na2SO4 mobile phase with 0.55 mL/L methanosulfonic acid as a pH modifier. The method was then validated by quantifying the concentration of acetic acid, formic acid, citric acid, and hydroxymethyl furfural (HMF) in pomegranate molasses, balsamic vinegar, and apple cider vinegar commercial products. The concentration of acetic acid and HMF in balsamic vinegar was 80.380 mg/mL (±1.272 mg/mL) and 2.153 mg/mL (±0.021 mg/mL), respectively. The apple cider vinegar was composed only of acetic acid with a concentration of 44.139 mg/mL (±0.053 mg/mL). The concentrations of citric acid and HMF were 123.425 mg/mL (±2.502 mg/mL) and 11.382 mg/mL (±0.582 mg/mL), respectively, in pomegranate molasses. Furthermore, this method is also capable of determining various organic acids and furans in biomass: levulinic acid, formic acid, furfurals, diformylfuran, and gamma-valerolactone

Characterisation of Italian and Dutch forestry and agricultural residues for the applicability in the bio-based sector

Knowing the accurate composition of biomass is of crucial importance in order to assess and decide on the use and processes to be applied to specific biomass types. In this study, the composition of the lignocellulosic constituents present in forestry, agricultural and under utilised waste residues was assessed. Considering the increased interest on hemicellulose fractions for application in biomaterials and biomolecules, large emphasis has been given in detailing the monomeric constituents of the hemicellulose polymer. Lignin and cellulose, the two other major components of lignocellulosic biomass, were analysed and correlated with the trends in the other constituents. In the samples analysed, the total structural sugars content ranged from 26.0 to 67.5% of the biomass dry weight, indicating high variation between different feedstock and fractions. Hemicellulose concentration and composition also varied significantly (from 38.8% in birch (Betula Pendula Roth) foliage to 22.0 % in rice (Oryza sativa L.) straw) between the feedstock types and within the same feedstock type between different species and different fractions. The extractives content varied greatly between the different species (from 2.66 % to 30.47 % of the biomass dry weight) with high contents in certain fractions of feedstock suggesting more detailed compositional analysis of these extracts is warranted

Fly ash from poultry litter gasification - can it be utilised in agriculture systems as a fertiliser?

Fly ash from a poultry litter gasification process and the potential of application of the fly ash as a fertiliser in line with the poultry litter protocol is investigated. The fines collected in the cyclone are mainly formed by ash which comprises between 70-83 wt.% of the fines on a dry basis, and to a lesser extent of carbon (elutriated char). The effect of the gasification operating conditions on the concentration of ash forming elements (inorganic compounds) in the fly ash, are discussed. In addition, the enrichment factor which defines the volatility, has been used and fly ash elements were categorised as Class I (non-volatile), Class II (semi-volatile with the possible occurrence of condensation) and Class III (highly volatile elements). Inorganic elements in fly ashes from poultry litter gasification experiments are categorised as Class I: Ca, Co, Cu, Fe, Hg, K, Mg, Mn, Na, Ni, P, Class II: Cd, Cr, Mo and Class III: Pb and Se. It has been found that the fly ash from the poultry litter gasification exceeds the upper acceptable limit set by Poultry Litter Protocol to be used as a fertiliser in agriculture system

Hydrogenation of sunflower oil over Pt-Ni bimetallic supported catalysts: preparation, characterisation and catalytic activity

It had been reported that in order to improve oil hydrogenation catalysts the geometric or electronic effects of the catalysts must be manipulated in order to achieve the desired activity or selectivity. To achieve this, the development of an active and selective bimetallic catalyst was undertaken. An innovative approach was taken to synthesize Pt-Ni catalysts supported on mesoporous silica using the surface redox reaction (Srr) technique. It was determined that the Srr preparation method resulted in better activity and lower selectivity towards trans than the traditional successive and co-impregnation bimetallic impregnation techniques. The change in selectivity can be explained by a promoter electronic effect generated by the close proximity of a second metal on the catalysts surface and from a geometric effect due to the incorporation of the Ni on the surface. All the bimetallic catalysts showed a drop in the formation of trans compared to the monometallic catalyst

Fly ash characterization from Cynara cardunculus L. gasification

This study analyzes the characteristics of fines produced during the air-blown gasification of Cynara cardunculus L. in a bubbling fluidized bed. These fines are collected by means of two hot cyclones and a hot filter. The gasification temperature is varied from 700 to 800 °C using olivine and magnesite as bed materials, with an equivalence ratio of 0.2. Relatively high carbon content is found in the entrained fines for all experiments. The lower heating value of the elutriated fines varies from 5.2 to 9.4 MJ/kgdb. Around 75% of the fines are captured in the first cyclone, 5% in the second cyclone, and the remaining 20% in the hot filter. The concentration of elements such as Se and Cl makes these fly ashes a hazardous material. Based on these properties the potential reuse of fly ashes is evaluated

Fly Ash Characterization from <i>Cynara</i> <i>cardunculus</i> L. Gasification

This study analyzes the characteristics of fines produced during the air-blown gasification of <i>Cynara cardunculus</i> L. in a bubbling fluidized bed. These fines are collected by means of two hot cyclones and a hot filter. The gasification temperature is varied from 700 to 800 °C using olivine and magnesite as bed materials, with an equivalence ratio of 0.2. Relatively high carbon content is found in the entrained fines for all experiments. The lower heating value of the elutriated fines varies from 5.2 to 9.4 MJ/kg_db. Around 75% of the fines are captured in the first cyclone, 5% in the second cyclone, and the remaining 20% in the hot filter. The concentration of elements such as Se and Cl makes these fly ashes a hazardous material. Based on these properties the potential reuse of fly ashes is evaluated