Preliminary Investigation into Expanded Resource Recovery through Paper Waste Fermentation as a Supplemental Feedstock for Anaerobic Digestion

As part of GLWA's biosolids master planning effort, anaerobic digestion is being evaluated to reduce the mass of material generated at the WRF and valorize the energy content of the sludge as biogas. However, understanding these capital investments are to serve the community for decades understanding how these assets could be enhanced or repurposed to align with shifting regulatory, environmental and market drivers is key to ensuring the right investments are made at the right time, building with a future in mind. One area GLWA is interested in is management of feedstocks for energy production which would result in co-digestion at the WRF. The practice of co-digestion, the digestion of sewage sludge with other organic feedstock, has proven to be a financial and environmental boon for the wastewater industry. Organic feedstock such as fats, oils and grease, food processing wastes and pre- and post-consumer food wastes have proven to be effectively digested by conventional anaerobic digestion systems. A partial list of facilities who have implemented in co-digestion is provide in Table 1, demonstrates the diversity of scopes of programs. The generation of biogas has been the path to energy neutrality for a number of utilities, including Gresham, OR, Johnstown-Gloversville, EBMUD and DTMA. At the same time there has been a significant shift in the industry to renewable natural gas production, as the associated renewable attributes (ex. Renewable Identification Numbers (RINs)) have significantly shifted the economic return on investment for biogas production. The challenge for co-digestion programs is that many of the feedstock are not considered cellulosic in nature, making their value lower the D5 rate verses the D3 for cellulosic materials. While this change has not necessarily resulted in a reduction in the co-digestion practice it opens fundamental questions around other opportunities to generate high-value biogas from anaerobic digestion of cellulosic waste products. Cellulosic materials such as paper, cardboard and newsprint are generated, used and discarded a part of daily life, often recycled or disposed of in landfills. The U.S. EPA estimated that paper and paperboard products represent approximately 67.4 million tons of the municipal solids waste stream, or about 23.1 percent, the largest fraction. In comparison food waste during the same period was 63.1 million tons or about 21.6 percent of the total mass of municipal solid waste. The management of wastepaper through anaerobic digestion for energy recovery and biosolids production if proven to be a viable technical and environmental solution, could provide a new means of leveraging infrastructure on a whole community basis by creating inter-agency waste management strategies for municipalities. To explore this for GLWA, a bench-scale trial was conducted utilizing a combination of pre-treatment at hyper-thermophilic temperatures, with and without C. bescii, to investigate fermentation potential and biochemical methane potential testing was used to understand the bioavailability of the treated feedstock at Western University in London, Ontario. Three paper sources were evaluated, copy paper, cardboard and newsprint, as representative paper wastes recovered from the municipal solid waste streams. The paper feedstocks were ground, Figure 1, prior to treatment. Treatments consisted of holding the paper slurry (water and paper) at 75 C, with and without C. bescii. The results of the BMP testing are presented in Figures, 2 and 3 for the photocopy paper and cardboard. What is apparent from the data is that the impact of pre-fermentation with C. bescii had mixed results. For the photocopy paper, pre-fermentation results in an increase in the rate of methane production, with maximum methane production achieved within 1.5 to 2 days of incubation, while the control reached a similar levels of methane production at greater than 4 days of incubation. For carboard, the total extent of methane production was much lower than photocopy paper, but the C. bescii were able to improve the overall yield of recovery by 65 percent. What the data suggests is that the incorporation of C. bescii, could be used to reduce reactor size, improve reactor efficiency or allow for diversified feedstock composition, mixed loads. However, newsprint proved to be more challenging substrate for pretreatment and anaerobic digestion. Specifically, the presence of significant levels of ink in the prepared slurry resulted in process inhibition, as noted in a reduced methane yield (Figure 3 a,b) relative to the washed samples (Figure 3 c,d). Interestingly, the C. bescii amended fermenters were less sensitive to the presence of the ink, showing elevated methane production relative to the control in both cases, with and without pre-washing. As utilities and municipalities look to manage waste streams and valorize materials they manage, there maybe opportunities to create synergies between solid waste and wastewater utilities. This paper will discuss not only the current means of valorization, methane production, but also potential other outlets. While significant additional research is required to reach a commercialized concept, these types of alternative feedstock investigations are critical to reshaping the waste management strategies of municipalities moving forward.