Case study: Zero liquid discharge in the pulp and paper industry

Feb. 5, 2024
The journey to cleaner, clearer, odor-free wastewater.

Meadow Lake Mechanical Pulp (MLMP), a subsidiary of Paper Excellence, operates Canada's only zero liquid discharge pulp facilities. Instead of releasing 6,500 cubic meter a day of wastewater into the receiving environment or the sewer, the mill recycles it, positioning MLMP at the forefront of water conservation in an industry under pressure to reduce its specific water intake (SWI) and specific effluent volume (SEV); the SEV for the pulp and paper industry is approximately 28 cubic meters of water per ton of product.

The mill faced quality issues in the water for reuse, characterized by elevated Chemical Oxygen Demand (COD) levels, green coloration and persistent odors. These factors negatively impacted the plant's reuse process and potentially, the quality of the pulp produced. A technological intervention was required to improve water quality and safeguard product quality.

The EBS-Di treatment technology from EnBiorganic Technologies was selected, after MLMP had tried using traditional bioaugmentation, wherein a limited amount of spore-state microbes and nutrients were applied periodically, to no avail.

The EBS-Di system is a microbial generator and dispensing unit that differs from traditional bioaugmentation because it is capable of autonomously and continuously generating and dispensing up to 720 litres of active state microbiology each day. The active state Bacillus microbes that it dispenses are adapted to the wastewater stream directly through the patent-pending processes of the EBS-Di. The proprietary formulation of Bacillus used are non-GMO and non-toxic certified organic ubiquitous soil bacteria, making them not only very safe for pulp and paper wastewater, but also very effective as they are natural consumers of the organic materials in pulp milling wastewater streams.

To assess the system's applicability and performance in the distinct environment of pulp and paper wastewater, a structured 6-month trial was initiated. The trial was supported by the Isle Advanced Industrial Trial Reservoir, a nonprofit innovation accelerator that de-risks trials by providing technical support and loan funding which only has to be repaid if the trial is a success.

Objectives

The technology trial at MLMP was designed with a clear set of objectives, or Critical Success Factors (CSFs). The trial was structured around a primary quantitative metric: the reduction of COD levels in the treated water – with the target of achieving a 30% reduction from the established baseline of 843 ppm COD for a continuous 6-week period, after acclimatization. This translated to bringing the COD levels down to 601 ppm, or lower.

In addition to this objective target, the trial also had subjective objectives. These included enhancements in perceived water color (removal of green coloration from algae), and elimination of problematic, perceptible odors. Achieving these subjective goals was important, as they directly impacted the production operational efficiency, and quality of the pulp produced.

The total trial period was 6 months, including set-up, commissioning, stabilization and steady state operation. Samples were analyzed weekly, taken from the storage reservoir from where water is taken for reuse in the pulp production process. Historical (2022) COD data from this location were analyzed and used as a pre-trial baseline.

Results

The trial period yielded a 6-month average COD level of 582 ppm, which was a 31% decrease from the baseline. As illustrated in the graph below, during the final 6-weeks of the trial period the COD levels dropped to an average of 395 ppm, a 53% COD reduction, surpassing the performance target and demonstrating the potential for the system's long-term effectiveness.

Qualitatively, MLMP observed transformative changes in the wastewater's characteristics. The water, once tainted with a greenish hue, indicative of algae proliferation and associated problems, now exhibited enhanced clarity and absence of color. Additionally, the odors were also substantially reduced.

These outcomes — both the substantial drop in COD levels and the perceptible improvements in water aesthetics and odor — served as clear indicators of the trial’s success. The dual achievement, in meeting and exceeding the objective target while also addressing the qualitative concerns, underscored the holistic impact on the reuse water. It confirmed that application of EnBiorganic’s process can solve even persistent and complex wastewater reuse challenges, such as those faced by MLMP.

Challenges

The execution of the EBS-Di trial at MLMP was not without challenges, the most prominent of which was the unexpected proliferation of Chlamydomonas algae. Chlamydomonas is a genus of green algae known for their adaptive capabilities, making them particularly tenacious in diverse environments. What caught the attention of the project team was the algae's resilience to thrive even in environments with limited sunlight, a characteristic not typically expected given its photosynthetic metabolism.

Compounding this challenge was MLMP's previous treatment strategy that involved the enrichment of wastewater ponds with nitrogen and phosphorus. Identifying the specific algae and recognizing the causal relationship between the nutrient addition and algal proliferation, EnBiorganic made a recommendation to stop the nutrient addition because EnBiorganic’s microbiology did not need the added nutrients. MLMP agreed and discontinued the addition of nitrogen and phosphorus to their treatment ponds.

This move proved decisive. Post the cessation of nutrient enrichment, there was a noticeable decline in the algae populations, which consequently led to a marked reduction in COD levels.

This adaptive strategy not only mitigated a major challenge but also reinforced the importance of a holistic understanding of wastewater treatment processes, emphasizing the need to regularly re-evaluate and adjust treatment strategies considering emerging challenges.

Conclusions

The trial set out to address the challenges of deteriorating water quality, particularly concerning COD levels, and enable treated wastewater reuse on site. Despite unforeseen challenges, such as the unexpected growth of Chlamydomonas, amplified by MLMP's initial treatment approach, adaptive measures ensured the project's success.

In the final 6 weeks of the trial, which served as the final assessment period, a 53% COD reduction was achieved. Beyond this quantitative success, observable enhancements in water clarity and odor enabling continued reuse of water from the lagoon. Simon Wiles, MLMP’s general manager, was satisfied that the trial has served its purpose, because “We’ve seen a great reduction in COD, odor, and an improved color to the water. The Trial program allowed EnBiorganic to demonstrate its bioaugmentation service to us, where before, with other vendors, we were trying to figure out it all on our own. Since then, for us operationally, it’s much better.”

The success of this trial is a testament to the collaborative spirit and innovation displayed by both MLMP and EnBiorganic. Given the successful outcome and achievement of critical success factors agreed upon prior to the start of the trial, MLMP has now committed to the continued use of the EBS-DI system for at least three years, based on a service business model. The company’s willingness to embrace a novel and environmentally conscious solution speaks volumes about their commitment to sustainable practices.

Speaking about the trial, EnBiorganic’s Anson Liski said “we are grateful for the opportunity provided by both Isle Utilities and Paper Excellence’s Meadow Lake Mechanical Pulp mill. This is an exciting new use-case for the EBS-Di and we look forward to growing into this industry over the coming months.”

The Advanced Industrial Reservoir is proud to have supported MLMP and EnBiorganic Technologies in the first successful trial for this reservoir initiative and looks forward to updates involving the EBS-Di technology.

Funded by the Isle Group and other sponsors, the Trial Reservoirs are sources of loan funding to accelerate the adoption of technologies that can help the water sector and adjacent industries adopt new methods and technologies, providing a risk-free opportunity to offer trials to potential end-users.