The increasing discharge of untreated wastewater poses risks to ecosystems and public health, necessitating sustainable treatment strategies. Anaerobic digestion (AD) of sewage sludge offers several benefits including waste-volume reduction and sludge stabilization. However, it produces nutrient-rich effluents, requiring further treatment. Microalgae can remove nutrients while generating valuable biomass. This study aimed to evaluate the effect of CO2 concentration and reactor configuration on the performance of Chlorococcum sp. cultivated in AD effluent of municipal sewage sludge. Four CO2 levels (0.04, 3, 6, and 9%) was tested and 6% CO2 yielded the highest biomass (0.98 g L− 1) and CO2 fixation rate (162 mg L− 1 d− 1), while maintaining ammonium and phosphorous removal comparable to aeration with 3 and 9% CO2. This concentration was used in ALR, BC, and BC with carriers. The highest nutrient removal was achieved in BC, with 37.61% NH4⁺-N and 25.87% phosphorus reduction, whereas growth in ALR reached the highest cell density (81 × 106 cells mL− 1) in 9 days. Biomass composition was stable across reactors, with similar protein, carbohydrate, or fatty acid methyl esters content. These findings demonstrate that the Nordic Chlorococcum sp. grown in AD effluent can remove NH4⁺-N and phosphorus across a wide CO2 range (0.04–9%). Culturing in ALR is the preferred option for rapid growth. However, BC offered better nutrient removal and higher biomass production but required longer cultivation than ALR.

This study investigates in-situ catalysis during fast co-pyrolysis of wood and plastic and focus on gases from the initial reactions. The materials were prepared through melt-mixing and include birch wood together with low-density polyethylene (LDPE), polypropylene (PP) or polystyrene (PS). The co-pyrolysis experiments were conducted at 600°C with a residence time of 5 seconds. Introduction of CaCO3 resulted in increased yields of the gaseous compounds. Notably, the amount of gaseous compounds increased from 14 to 27 wt% for Wood-LDPE, from 17 to 31 wt% for Wood-PP, and from 44 to 81 wt% for Wood-PS. Particularly, compounds with a carbon number below 10 showed the most significant increase. This study contributes to a better understanding of the initial reactions of fast co-pyrolysis of wood and plastic. Specifically, it includes the impact of in-situ inorganic catalysts.

Bio-oil derived from fast pyrolysis of wood contains oxygenates and has a relatively low heating value. These are challenges that need to be tackled if wood-derived bio-oil is to be used as drop-in fuels. The bio-oil can be obtained by condensation of gaseous products. Using a material with no oxygen in addition to wood during fast pyrolysis could be a technique to reduce the formation of oxygenates and promote a hydrocarbon-rich product. This work aims to evaluate the primary gaseous products formed during fast co-pyrolysis of birch wood and plastic. The pyrolysis was performed in a micropyrolyser at 600 °C with a residence time of 5 s. Birch wood and plastic were melt-mixed at different weight ratios to study possible interaction effects upon pyrolysis. The different plastics used were low-density polyethylene (LDPE), polypropylene (PP) and polystyrene (PS). The total gaseous product was between 10–20 wt% from Wood-LDPE or Wood-PP, while it was in the range 15–90 wt% from Wood-PS. The analysis of gas product found that the formation of oxygenates (up to 9 wt%) was lower than expected (up to 14 wt%) for the mixtures of wood and plastic compared to the pure materials (about 18 wt%). The reduction of oxygenates (up to 90 %) was mainly due to a lower production of ketones, carboxylic acids and aldehydes. Maximum hydrocarbons in the gas phase from binary mixtures were around 8, 15 and 55 wt% from Wood-LDPE, Wood-PP and Wood-PS, respectively. The most significant difference between experimental and estimated values assuming no interaction among hydrocarbons was observed in the case of alkenes and alkanes for Wood-LDPE, as well as alkanes for Wood-PS, while the Wood and PP mixture showed almost no signs of interaction. This work is beneficial for understanding interactions between wood and plastics, and could be used to reduce the amount of oxygenates from wood pyrolysis and reduce the need for upgrading.

Anaerobic digestion is a promising method for organic waste treatment. While the obtained digestate can function as fertilizer, the liquid fraction produced is rather problematic to discharge due to its high nitrogen and chemical oxygen demand contents. Microalgae have great potential in sustainable nutrient removal from wastewater. This study aimed at evaluating native Swedish microalgae cultivation (batch operation mode, 25°C and continuous light of 80 μmol m−2 s−1) on anaerobic digestion effluent of pulp and paper sludge (PPS) or chicken manure (CKM) to remove ammonium and volatile fatty acids (VFAs). While algal strains, Chlorella vulgaris, Chlorococcum sp., Coelastrella sp., Scotiellopsis reticulata and Desmodesmus sp., could assimilate VFAs as carbon source, acetic acid was the most preferred. Higher algal biomass and cell densities were achieved using PPS compared to CKM. In PPS, Coelastrella sp. and Chlorella vulgaris reached the highest cell densities after 15 days, about 79 × 106 and 43 × 106 cells mL−1, respectively. Although in PPS, ammonium was completely assimilated (195 mg L−1), this was only 46% (172 mg L−1) in CKM. Coelastrella sp. produced the highest biomass concentration independently of the medium (1.84 g L−1 in PPS and 1.99 g L−1 in CKM). This strain is a promising candidate for nutrient removal and biomass production in the aforementioned media, followed by Chlorella vulgaris and Chlorococcum sp. They have great potential to reduce the environmental impact of industrial anaerobic digestion effluents in Nordic countries.

The treatment of organic waste using anaerobic digestion is a promising and well-matured organic waste management method. However, the effluent from anaerobic digestion has a significant discharge risk due to its high ammonium content. Microalgae could be a valuable solution to remove this nitrogen. This work aimed at evaluating the growth of three Nordic microalgae strains (Chlorella vulgaris, Chlorococcum sp. and Coelastrella sp.) in different concentrations of effluent from anaerobic digestion of municipal sewage sludge. None of the strains was able to grow in effluent diluted two times (X2) or three times (X3) due to the high ammonium content (600 and 400 mg L−1, respectively). While Chlorococcum sp. showed a lag phase of 7 and 11-days in 5 times (X5) and 7 times (X7) diluted effluent, respectively, this strain demonstrated 53 % and 86 % total ammonia nitrogen (TAN) removal efficiency after 15 days; in X10 its TAN removal was 100 %. Without any lag phase Coelastrella sp. showed the same TAN removal efficiencies in X5 and X7 as Chlorococcum sp. However, C. vulgaris had the highest TAN removal in X5 (90%) and X7 (90%). Furthermore, this strain showed the highest amount of biomass dry weight production in all media (1.1 g L−1 in X5). Therefore, C. vulgaris and Chlorococcum sp. are promising candidates for nitrogen removal and sustainable algae biomass production, resulting in mitigating the environmental issues of anaerobic digestion effluents in Nordic countries through the conversion of waste streams into resources.

In this study, predominant bacterial and archaeal populations and their roles during anaerobic mono-digestion of food waste (FW) and co-digestion of FW with straw pellets (SP) at thermophilic temperature (53 ± 1 °C) were assessed by Next Generation Sequencing (NGS) analysis at organic loading rates (OLRs) of 3.0 and 7.0 gVS/L/d. Depending on the seed; results revealed that Firmicutes, Bacteroidetes, and Proteobacteria were, respectively the most prevalent bacterial phyla at both OLRs investigated. On the other hand, Euryarchaeota was dominated by methanogens playing crucial role in biogas production and correlated mainly with the activities of Methanobacteria and Methanomicrobia at class level. Acetoclastic Methanosaetae was the predominant genus at OLR = 3.0 gVS/L/d; however, shared the same predominance with hydrogenotrophic methanogens Methanospirillium at the highest OLR. Although no clear effect in response to straw addition at OLR of 3.0 gVS/L/d could be seen in terms of methanogenic archaea at genus level, hydrogenotrophic methanogens revealed some shift from Methanobacterium to Methanospirillium at higher OLR. Nevertheless, no prominent microbial shift in the presence of wheat straw at increased OLR was likely due to adapted inoculation at start-up which was also demonstrated by relatively stable biogas yields during co-digestion.

A high load of inorganics in raw lignocellulosic biomass is known to inhibit the yield of bio-oil and alter the chemical reactions during fast pyrolysis of biomass. In this study, palm kernel shell (PKS), an agricultural residue from palm oil production, and two other woody biomass samples (mahogany (MAH) sawdust and iroko (IRO) sawdust) were pretreated with distilled water or an acidic solution (either acetic, formic, hydrochloric (HCl) or sulfuric acid (H2SO4)) before fast pyrolysis in order to investigate its effect on the primary products and pyrolysis reaction pathways. The raw and pretreated PKS, MAH and IRO were pyrolysed at 600 °C and 5 s with a micro-pyrolyser connected to a gas chromatograph–mass spectrometer/flame ionisation detector (GC-MS/FID). Of the leaching solutions, HCl was the most effective in removing inorganics from the biomass and enhancing the primary pyrolysis product formed compared to the organic acids (acetic and formic acid). The production of levoglucosan was greatly improved for all pretreated biomasses when compared to the original biomass but especially after HCl pretreatment. Additionally, the relative content of the saccharides was maximised after pretreatment with H2SO4, which was due to the increased production of levoglucosenone. The relative content of the saccharides increased by over 70%. This increase may have occurred due to a possible reaction catalysed by the remaining acid in the biomass. The production of furans, especially furfural, was increased for all pretreatments but most noticeable when H2SO4 was used. However, the relative content of acids and ketones was generally reduced for PKS, MAH and IRO across all leaching solutions. The relative content of the phenol-type compound decreased to a large extent during pyrolysis after acid pretreatment, which may be attributed to dehydration and demethoxylation reactions. This study shows that the production of valuable chemicals could be promoted by pretreatment with different acid solutions.

Co-pyrolysis is one possible method to handle different biomass leftovers. The success of the implementation depends on several factors, of which the quality of the produced bio-oil is of the highest importance, together with the throughput and constraints of the feedstock. In this study, the fast co-pyrolysis of palm kernel shell (PKS) and woody biomass was conducted in a micro-pyrolyser connected to a Gas Chromatograph–Mass Spectrometer/Flame Ionisation Detector (GC–MS/FID) at 600 °C and 5 s. Different blend ratios were studied to reveal interactions on the primary products formed from the co-pyrolysis, specifically PKS and two woody biomasses. A comparison of the experimental and predicted yields showed that the co-pyrolysis of the binary blends in equal proportions, PKS with mahogany (MAH) or iroko (IRO) sawdust, resulted in a decrease in the relative yield of the phenols by 19%, while HAA was promoted by 43% for the PKS:IRO-1:1 pyrolysis blend, and the saccharides were strongly inhibited for the PKS:MAH-1:1 pyrolysis blend. However, no difference was observed in the yields for the different groups of compounds when the two woody biomasses (MAH:IRO-1:1) were co-pyrolysed. In contrast to the binary blend, the pyrolysis of the ternary blends showed that the yield of the saccharides was promoted to a large extent, while the acids were inhibited for the PKS:MAH:IRO-1:1:1 pyrolysis blend. However, the relative yield of the saccharides was inhibited to a large extent for the PKS:MAH:IRO-1:2:2 pyrolysis blend, while no major difference was observed in the yields across the different groups of compounds when PKS and the woody biomass were blended in equal amounts and pyrolysed (PKS:MAH:IRO-2:1:1). This study showed evidence of a synergistic interaction when co-pyrolysing different biomasses. It also shows that it is possible to enhance the production of a valuable group of compounds with the right biomass composition and blend ratio. 

This study aimed to establish primary reactions and identify gaseous products during fast pyrolysis of low-density polyethylene (LDPE), polypropylene (PP) and polystyrene (PS). Fast pyrolysis was performed by using Py-GC/MS/FID at 574 ± 22 °C for 5 s. Gaseous fractions formed during pyrolysis of LDPE, PP and PS were 14 ± 1 wt%, 31 ± 3 wt% and 103 ± 12 wt%, respectively. The main gaseous compounds from LDPE were butane, 1-pentane and 1-hexene. PP pyrolysis gave propene, pentane and 2,4-dimethyl-1-heptene as the main gaseous compounds. Styrene monomer was the dominant gas from PS. The results showed that polyolefin (PP and PE) produced aliphatic hydrocarbons, while PS formed aromatic hydrocarbons. Furthermore, the proposed mechanism suggests that both inter- and intra-molecular hydrogen transfer occur during PP and PE pyrolysis. PS pyrolysis involves a C-C cleavage at the aliphatic side chain. This work is important to understand the mechanism of gas formation of primary reactions from pyrolysis of common plastics.

Fast pyrolysis is an industrially attractive method to produce fuels and chemicals from biomass; however, to gain better control over the process, the reactions and interactions between the components and decomposition products need elucidation. This study investigated primary reactions during fast pyrolysis of biomass. Pyrolysis of the three main biomass components (cellulose, hemicellulose and lignin) and their blends was carried out with a micro-pyrolyser connected to a Gas Chromatograph-Mass Spectrometer/Flame Ionisation Detector (GC–MS/FID). The blends of the individual components were prepared in similar proportions to that of native biomass (birchwood) and were pyrolysed at 600 °C for 2 s. The results showed that the two-component blends decrease the production of saccharides to a large extent. This was especially noticeable for levoglucosan when cellulose was mixed with either hemicellulose or lignin. Similarly, in the presence of cellulose, the formation of phenolic compounds from lignin was inhibited by 62 %. However, no differences were found in yields of the main products for the xylan-lignin blend compared to those from the individual components. The yields of volatile products from the cellulose-xylan blend were promoted for a majority of the product categories and were most pronounced for the aldehydes. Furthermore, while the formation of the phenols and saccharides was slightly inhibited for the three-component blend, the aldehydes, ketones and furans showed an increased production compared to the weighed sum of products expected, based on the pyrolysis of the individual components. The native biomass showed a similar trend as the three-component blend in all product categories except for the saccharides, which were inhibited to a large extent. This study provides a better understanding of the interactions occurring between different components during fast pyrolysis of biomass.