Environmental analysis of producing biochar and energy recovery from pulp and paper mill biosludge

Abstract

Sweden is one of the largest exporters of pulp and paper products in the world. It follows that huge quantities of sludge rich in carbonaceous organic material and containing heavy metals are generated. This paper carried out a comparative environmental analysis of three different technologies, which can be adopted to produce biochar and recover energy from the biosludge, using landfilling as the reference case. These three thermochemical biosludge management systems—using incineration, pyrolysis, and hydrothermal carbonization (HTC)—were modeled using life cycle assessment (LCA). Heat generated in the incineration process (System A) was considered to be for captive consumption within the kraft pulp mills. It was assumed that the biochars—pyrochar and hydrochar—produced from pyrolysis (System B) and HTC (System C), respectively, were added to the forest soils. The LCA results show that all the alternative systems considerably improve the environmental performance of biosludge management, relative to landfilling. For all systems, there are net reductions in greenhouse gas emissions (–0.89, –1.43, and –1.13 tonnes CO2‐equivalent per tonne dry matter biosludge in Systems A, B, and C, respectively). System B resulted in the lowest potential eutrophication and terrestrial ecotoxicity impacts, whereas System C had the least acidification potential. The results of this analysis show that, from an environmental point of view, biochar soil amendment as an alternative method for handling pulp and paper mill biosludge is preferable to energy recovery. However, an optimal biochar system needs to factor in the social and economic contexts as well.

A Review of the Chemistry of Anaerobic Digestion: Methods of Accelerating and Optimizing Process Efficiency

“…A consequence of the strong interrelationships between the various aspects of AD is the advances so far made in the optimization of the technology such that research on only one aspect may not be technically reliable hence the need for studies to be conducted on other aspects of the technology. Digester design innovations, recycling of digested slurry, the use of other non-biological conductive materials like biochar (a solid product of thermal decomposition of biomass) to improve AD and digestate as well as the ability to co-digest different feedstocks are some of the recent advances made in the AD technology [111][112][113][114][115][116][117][118][119]. The use of composite materials such as magnetic fly ash (Fe 3 O 4 /FA) for pretreatment of mainly livestock manure used as feedstock in AD processes [78] are among some of the other recent advances made in optimization of AD systems but the economic viability of this pretreatment method is yet to be determined.…”

Hydrochar-Amended Substrates for Production of Containerized Pine Tree Seedlings under Different Fertilization Regimes

“…Similarly, Liu et al [56] found that exchangeable and reducible fraction of heavy metals in sewage sludge decreased by hydrothermal carbonization. The immobilized heavy metals in hydrochar considerably reduce the terrestrial ecotoxicity [24] and aquatic ecotoxicity impacts [25] of soil application of biochar.…”

“…Moreover, peat use reduction due to replacement with hydrochar will result in less peat extraction and, therefore, will decrease the associated environmental impacts. Results of our previous studies showed that pyrochar and hydrochar production from paper mill sludge can significantly increase the environmental performance of sludge management and contribute to sustainable forest ecosystems [24,25]. Hydrochar-amended substrates can contribute to climate change mitigation with carbon sequestration as part of the normal reforestation.…”

“…Biochar from paper sludge has also been characterized with high specific surface area [22] and has shown promising effect on simulating growth of plants such as Lolium perenne [23]. Biochar from pulp and paper mill sludge has been reported to have higher environmental performance relative to conventional disposal methods for sludge such as landfilling or incineration [24,25]. In many studies, the term 'biochar' is generally understood to mean 'pyrochar', which is a coproduct of fast pyrolysis or gasification.…”

Original article: fermented pulp and paper bio-sludge as feed for black soldier fly larvae

“…PPBS consists of lignocellulose material from the pulp and paper process [12], heavy metals [13,14], as well as bacterial cells from the wastewater treatment. The composition of PPBS varies depending on the paper mill process and wastewater treatment, but typically it contains crude protein 1.5-8.3%, fat 0.3-3.3%, dry substance (DS) 10-30%, lignin 17-40% DS, nitrogen 18,000-84,000 mg/kg DS, phosphorus 1700-21,000 mg/kg DS, potassium 200-4600 mg/kg DS, and ash (27% DS) [13,15].…”