Abstract
Waste-to-energy or value-added products have been increasingly considered in many pulp and paper mills (PPMs) worldwide. However, developing appropriate conversion technologies are a major challenge in transforming PPMs wastes into biofuels or value-added biomaterials. In the present study, a long term (320 d) anaerobic digestion of primary sludge of a thermomechanical pulp mill (TMP) was carried out for the first time in a thermophilic anaerobic membrane bioreactor (ThAnMBR). Effect of organic loading rate (OLR) in the range of 2.5–6.8 kg COD/m3 d and hydraulic retention times (HRT) of 3–8 d on the process performance was investigated. Under various OLRs, stable biogas productions were obtained, and the best results were achieved with lower OLR (2.5 kg COD/m3 d) and higher HRT (8 d), at biogas yields of 189 L biogas/kg MLSS fed. However, it was found that the biogas production and sludge biomass degradation decrease when the organic loading rate increases. The proportion of sludge reduction ranged from 28.9 to 46.7% depending on the applied OLRs. Despite varying OLRs, stable membrane performance was obtained, where the required membrane flux was easily maintained during the reactor operation. In this study, also the properties of digestate and membrane permeates were studied under different operating conditions, and they fluctuated to some extent with OLR. ThAnMBR is a promising new technology for pulp and paper mill primary sludge treatment.Graphic abstract
Highlights
Pulp and paper mill sludge (PPMS) represents a large part of the industrial waste and contains a high portion of the organic matter (Elliott and Mahmood, 2012)
Phase I was operated at hydraulic retention times (HRT) of 5 d and organic loading rate (OLR) of 3.7 kg-COD/m3 d, while phases II and III were operated at HRTs of 3 and 8 d and OLRs of 6.8 and 2.59 kg-COD/m3 d, respectively
This study aims to test the feasibility of the primary sludge digestion under relatively higher organic loading rates and lower HRTs
Summary
Pulp and paper mill sludge (PPMS) represents a large part of the industrial waste and contains a high portion of the organic matter (Elliott and Mahmood, 2012). Sludge waste is produced from both virgin and recycled paper production processes (Simão et al, 2018). This substrate is usually undesirable and needs to be treated or disposed of in an environmentally acceptable manner. The common handling strategies of the waste sludge are landfilling, incineration, and recycling in the paper making process. Kraft PPM primary sludge is composed of woody materials such as cellulose (58 wt%), hemicelluloses (12 wt%), and lignin (20 wt%), along with inorganic materials that have been used in the pulping process (Bayr and Rintala, 2012). The application of traditional sludge treatment processes leads to the loss of these precious resources accompanied by environmental pollution (Bayr et al, 2013; Hazarika and Khwairakpam, 2018)
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