Pyrolysis of organic side stream materials for the production of biochar as an amendment in green roofs: Characterization and field experiments

Green roofs offer a solution to worldwide problems in cities like: the urban heat island effect, floods and the loss of rural regions. Nevertheless, the widespread application of green roofs still faces some serious challenges, e.g. an excessive amount of drainage water, an excess of nutrients in this water, and plant mortality in periods of severe drought. Also, the production process of the components of these substrates, such as expanded clay, is not environmentally and energy-friendly. Biochar amendment in green roof substrates can help to overcome these problems because of its valuable properties like a high nutrient content, high waterholding capacity (WHC), low density and its self-sustaining production process. In this research, biochar is produced from six different side streams in a pilot-scale rotating kiln carbonization reactor (kg/hour input). These side streams consists out of: MDF, date palm, coffee skins, tree bark, olive stones and a waste wood mix. The produced biochars are characterized with multiple physico-chemical analyses like biochar yield, elemental composition, surface functional groups, morphology, WHC, cation exchange capacity and polyaromatic hydrocarbons (PAH’s). Furthermore, a techno-economical analysis is performed on the large-scale production of these biochars. Small scale (0,25 m2) and field experiments (2.5 m2) with biochar incorporated in commercially available green roof substrates in the temperate climate of the Netherlands and Belgium examine whether biochar can offer a solution to the described problems. Based on the analyses of the biochar, in particular the PAH’s and elemental composition, and the small scale growth experiments, two different biochars made from the waste wood mix and tree bark in concentrations of 1 and 5 % are selected for the field experiments. Growth of Sedum plants is monitored with digital imaging processing over a period of several months, starting from November 2018. Several chemical and physical parameters are monitored and linked to the properties of the biochar incorporated substrate like pH, conductivity, nutrient leaching and waterholding capacity

Biochar characterization of raw versus spent common ivy: Inorganic nutrient behavior

Hedera sp., common Ivy, a lignocellulosic evergreen vine, is commonly seen in gardens and yards all over the globe. It is an excellent candidate to be applied in vertical green walls to improve ecosystems in future green cities (e.g. fine particulate matter adsorption). These green walls need to be trimmed regularly, thus leaving a major residue stream which could be promising as biomass feedstock for biochar fertilizer production. However, common Ivy contains valuable compounds (e.g. etheric oils and triterpene saponins) increasing the process’ added value. These should preferably be extracted prior to thermal conversion. The aim of this study is therefore to investigate the influence of extraction methods on the final properties of common ivy’s biochar using conventional pyrolysis. Investigated extraction methods include a Soxhlet ethanol extraction and a steam distillation, to obtain respectively a triterpene saponin and volatile oil extract. The influence of these extractions on the biochar properties was studied by comparing the thermal conversion and biochar properties of spent, extracted, biomass with raw biomass. Studied properties include biochar yield, elemental composition (CHNO), amount of inorganic nutrients, specific surface area, and presence of harmful heavy metals. The guidelines of the European Biochar Certificate are used to evaluate said properties. Furthermore, the pyrolysis process parameters, temperature and heating rate, were optimized to improve said biochar properties for application as fertilizer. Tested pyrolysis temperatures were 400, 550 and 700 °C. Results show that biochar yield from raw ivy was inversely proportional with pyrolysis temperature ranging from 29.6 ± 0.6% at 400 °C, 25.4% ± 0.03 at 550 °C and 23.0 ± 0.06 % at 700 °C. It was found that steam distillation lowers the amount of heavy metals in the material, whilst the inorganic nutrients are retained, thus enhancing the biochar’s potential as fertilizer. Furthermore, nitrogen content remained constant, around 2%, before and after pyrolysis both for raw and spent ivy, these results indicate that high-quality biochars were produced. To further understand biochar’s chemical behavior in soils, structural properties and morphology are being investigated further, specific surface area via BET, general pore structure using SEM, surface functional groups with FT-IR and, aromaticity with CP/MAS 13C NMR results will be presented accordingly

Bio-based poly(3-hydroxybutyrate)/thermoplastic starch composites as a host matrix for biochar fillers

Biochar is an excellent, but less-used candidate to serve as an alternative filler in poly(3-hydroxybutyrate) (PHB)-based composites. Increasing amounts of biochar between 20 and 50 wt% were incorporated in PHB/char and PHB/thermoplastic starch (TPS)/char composites and its effects on the microstructure, crystallization and thermal properties were investigated. PHB shows a significant reduction in molecular weight after processing and the increasing amounts of biochar decreases this even stronger. From thermogravimetric analysis, it was clear that the onset degradation temperature of the PHB/char composites (255 °C) is only slightly influenced by the biochar particles up to 40 wt%. Contrastingly, this temperature reduces to 245 °C when 50 wt% of biochar is added. Additional data confirm that morphology and crystallization kinetics are enhanced up to 40 wt% of biochar, while even higher percentages of filler clearly have an opposite effect. Finally, this work reveals the ability of TPS to work as an excellent intermediator between biochar and PHB at biochar concentrations up to 20 wt%, where degradation and resulting reduction in molecular weight remains limited as compared to that of the PHB/char sample. Furthermore, like biochar, TPS acts as a nucleation agent in the composites and removes the influence of the biochar on the thermal stability of the composites

Poly (lactic acid) bio-composites containing biochar particles: effects of fillers and plasticizer on crystallization and thermal properties

Biochar has emerged as a filler material for bio-degradable composites with favorable thermal and mechanical properties. Therefore, biochar is used in poly (lactic acid) (PLA) and PLA/thermoplastic starch (TPS) based composites. The crystallization and thermo-analytical properties of these blends with increasing amounts (20 to 50 wt%) of biochar are investigated. In the thermogravimetric analysis, the PLA/char composites’ onset degradation temperature and temperature of maximum weight loss decrease with increasing biochar concentrations (320 to 275 °C and 380 to 350 °C, respectively). Contrastingly, in the PLA/TPS/char composites, the impact of the biochar is shielded by the TPS. The unaltered glass transition demonstrates that biochar does not act as a plasticizer in any of the composites, while TPS does. Biochar acts as a nucleation agent, but hinders further crystal growth at high concentrations, as confirmed by isothermal crystallization and infrared spectroscopy. The TPS smoothens the PLA/biochar interface, leading to an obstructed nucleation effect of biochar, proven by differential scanning calorimetry, infrared spectroscopy, and scanning electron microscopy. This work demonstrates the shielding effect TPS has on biochar and can help to understand further and optimize the production and biodegradability of these composites

An Experimentally Validated Selection Protocol for Biochar as a Sustainable Component in Green Roofs

Green roofs contribute to more sustainable cities, but current commercial substrates suffer from important limitations. If carefully selected, biochar could serve as a viable option for a more sustainable green roof substrate. We propose a protocol to select an optimal biochar for green roof substrate amendment. Coffee husks, medium-density fiberboard, palm date fronds, and a mixture of waste wood, tree bark, and olive stone kernels are selected as residues for biochar production to develop a selection protocol. The residues are pyrolyzed at 350, 450, 500, and 550 °C in a lab-scale reactor. A pyrolysis temperature of 450 °C is selected for upscaling and is based on biochar yield, pH, salinity, and elemental composition. From evaluating the biochar characteristics after upscaling, it can be concluded that the biochar’s carbonization degree is mainly controlled by pyrolysis temperature, while yield, pH, and salinity are more dependent on the biomass properties. Ultimately, our procedure evaluates the presence of important contaminants, the biochar’s water holding capacity, salinity, pH, and carbonization degree. To validate the developed protocol, plant coverage experiments on green roofs are performed, which are quantified using a novel digital image processing method, demonstrating its efficient use to facilitate future biochar selection in substrates

Characterisation of two wood-waste and coffee bean husk biochars for the removal of micropollutants from water

The inclusion of bioaugmented low-cost biochar in current wastewater treatment technologies is a promising way to enhance the removal and degradation of emerging contaminants. In this paper, the properties of two wood waste biochars (wood waste mix - AB, and date palm fiber wood - PDF), and coffee bean husks (COF), produced at four temperatures (350, 450, 500, 550 degrees C) were compared, and investigated in the presence of Geobacter sulfurreducens or a mixed freshwater stream bacterial culture to understand their potential for the adsorption and biotransformation of two types of pesticides (thiacloprid, pirimicarb), and two pharmaceuticals (ibuprofen, diclofenac). Biochar yield was similar for all three biochars and ranged between 30 and 35%. The ash content of PDF and COF was significantly higher than AB. pH and electrical conductivity (EC) were initially high for COF (pH: 7.4-8; EC: 3-4.27 mS/cm) and PDF (pH: 7.7-10.1; EC: 4-6.24 mS/cm) after 24 h, but stabilized at neutral pH and <0.5 mS/cm EC after additional washes. COF and AB did not leach high concentrations of chloride (<10 mg/L), nitrate (<1 mg/L), nor sulphate (<76 mg/L), this in contrast to date palm fiber wood (PDF) with 1760 mg/L Cl- (550 degrees C), and 846 mg/L sulphate (350 degrees C). Lower pyrolysis temperatures reduced leachable anions. The biochars were highly (ultra)microporous with little meso- and macroporosity. The adsorption experiments showed that AB and COF biochars were both suited to sorb more than 90% of the initially spiked 10 ppm pirimicarb, AB removed 50.2% of the initial diclofenac concentration compared to only 5% for the no-biochar control, and both biochars could remove about 55% of the initially spiked thiacloprid, and 40% of the ibuprofen. In the presence of a mixed culture, on average 30% more thiacloprid and ibuprofen was removed from the supernatant by AB and COF than the sterile control. This work shows that selected wood-waste feedstocks and low pyrolysis temperature can produce environmentally-safe biochars that have suitable characteristics to sorb emergent pollutants from water. These materials could be further studied in multi-pollution sorption/competition experiments, and in larger environmental wastewater treatment systems

DataSheet1_Characterisation of Two Wood-Waste and Coffee Bean Husk Biochars for the Removal of Micropollutants from Water.docx

The inclusion of bioaugmented low-cost biochar in current wastewater treatment technologies is a promising way to enhance the removal and degradation of emerging contaminants. In this paper, the properties of two wood waste biochars (wood waste mix - AB, and date palm fiber wood - PDF), and coffee bean husks (COF), produced at four temperatures (350, 450, 500, 550°C) were compared, and investigated in the presence of Geobacter sulfurreducens or a mixed freshwater stream bacterial culture to understand their potential for the adsorption and biotransformation of two types of pesticides (thiacloprid, pirimicarb), and two pharmaceuticals (ibuprofen, diclofenac). Biochar yield was similar for all three biochars and ranged between 30 and 35%. The ash content of PDF and COF was significantly higher than AB. pH and electrical conductivity (EC) were initially high for COF (pH: 7.4–8; EC: 3–4.27 mS/cm) and PDF (pH: 7.7–10.1; EC: 4–6.24 mS/cm) after 24 h, but stabilized at neutral pH and − (550°C), and 846 mg/L sulphate (350°C). Lower pyrolysis temperatures reduced leachable anions. The biochars were highly (ultra)microporous with little meso- and macroporosity. The adsorption experiments showed that AB and COF biochars were both suited to sorb more than 90% of the initially spiked 10 ppm pirimicarb, AB removed 50.2% of the initial diclofenac concentration compared to only 5% for the no-biochar control, and both biochars could remove about 55% of the initially spiked thiacloprid, and 40% of the ibuprofen. In the presence of a mixed culture, on average 30% more thiacloprid and ibuprofen was removed from the supernatant by AB and COF than the sterile control. This work shows that selected wood-waste feedstocks and low pyrolysis temperature can produce environmentally-safe biochars that have suitable characteristics to sorb emergent pollutants from water. These materials could be further studied in multi-pollution sorption/competition experiments, and in larger environmental wastewater treatment systems.</p