Key Takeaways & Executive Findings
- •• • Corncob-based carbon sources with PHBV:cellulose ratio of 1:1 (CC4) achieved release durations exceeding 134 h, ensuring stable carbon supply for denitrification, outperforming straw and sawdust systems in bioavailability. • • Increasing straw or sawdust proportion (e.g., PHBV:cellulose ratio from 4:1 to 4:5) accelerated release rates and increased total DOC release, while reducing aromaticity (SUVA254) and molecular weight, enhancing DOM bioavailability. • • Optimal formulations JG5, MX5, and CC4 exhibited low theoretical maximum release (M∞) and high mass transfer coefficients (k), balancing sustained release and availability, critical for long-term denitrification. • • EEM-PARAFAC revealed that protein-like components (C1, C2) dominated released DOM, with relative abundance far exceeding humic-like C3; higher straw/sawdust ratios promoted simultaneous release of both protein-like and humic-like substances, while corncob ratio had minimal effect on component distribution.
Abstract
Low C/N ratios in wastewater treatment plant effluent necessitate external carbon sources for denitrification, but conventional liquid carbon sources are costly and unstable. This study prepared nine composite solid-phase carbon sources by combining PHBV with natural cellulose materials (straw, sawdust, corncob) at different mass ratios. Dynamic release experiments, DOC analysis, UV-Vis spectroscopy, and EEM fluorescence were employed to characterize carbon release. Results showed that increasing cellulose proportion in corncob-based sources led to release patterns opposite to those of straw- and sawdust-based sources. For straw and sawdust, higher cellulose ratios accelerated release rates, increased total release and duration, reduced aromaticity and molecular weight of released DOM, and promoted protein-like components (tryptophan, tyrosine), indicating enhanced bioavailability. Under identical ratios, corncob-based sources exhibited moderate total release, release durations exceeding 134 h, lower DOM aromaticity and molecular weight, and lower humic substance proportion, indicating superior bioavailability and engineering potential. Among the nine sources, JG5, MX5, and CC4 (PHBV:cellulose mass ratios of 4:5, 4:5, and 1:1, respectively) showed optimal comprehensive performance with low theoretical maximum release, long release periods, and high mass transfer coefficients. EEM-PARAFAC identified three DOM components (protein-like C1, C2; humic-like C3), with protein-like components dominating. This study validates the relationship between cellulose proportion and release kinetics and reveals synergistic regulation of DOM components, offering guidance for designing effective solid-phase carbon sources.
1. Introduction
Municipal wastewater treatment plant effluent frequently exhibits low C/N ratios (<5), impairing heterotrophic denitrification and necessitating external carbon supplementation. Traditional liquid carbon sources such as sodium acetate and glucose offer high bioavailability but suffer from high cost, difficult dosage control, and potential water quality fluctuations, limiting their systematic application. Solid-phase carbon sources, including natural cellulose (e.g., straw, sawdust, corncob) and biodegradable polymers (e.g., PHBV, PCL, PLA), have emerged as alternatives, providing slow carbon release and serving as biofilm carriers. However, natural cellulose alone often releases carbon too rapidly with short durations, while polymers release steadily but at high cost. Composite materials combining these components aim to balance performance and cost.
This study addresses the bottleneck by systematically preparing nine composite solid-phase carbon sources with varying PHBV-to-cellulose mass ratios using straw, sawdust, and corncob. Through dynamic release experiments and spectroscopic characterization, we elucidate how material composition influences release kinetics and DOM quality. The findings reveal that corncob-based composites exhibit superior sustained release and bioavailability, offering a cost-effective solution for low C/N denitrification. This work provides a rational basis for designing solid-phase carbon sources with optimized release profiles, advancing their practical application in wastewater treatment.
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ZHU Shenghui, ZHOU Gang, ZHU Ye, MIAO Lingzhan, HOU Jun (2026). Preparation of Solid-Phase Carbon Sources with Different Ratios and Their Carbon Release Properties. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202604007
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Frequently Asked Questions
What are the failure mechanisms of these composite carbon sources under prolonged operation or varying hydraulic conditions?
The study indicates that natural cellulose components like straw and sawdust can cause rapid initial release and shortened lifespan, while PHBV provides stable release. Under prolonged operation, depletion of cellulose may lead to reduced release rates, and biofilm clogging could occur. The optimal ratios (e.g., CC4) were designed to mitigate these issues, achieving release durations over 134 h, but long-term stability beyond this period requires further investigation.
How does the cost of corncob-based composites compare with conventional liquid carbon sources and other solid-phase systems?
Corncob is an agricultural waste, making it low-cost and readily available. PHBV is more expensive, but the composite approach reduces PHBV content while maintaining performance. Compared to liquid carbon sources like sodium acetate, solid-phase systems eliminate continuous dosing costs and reduce operational complexity. The study does not provide a full economic analysis, but the use of waste biomass suggests significant cost savings potential.
What are the scalability bottlenecks for industrial-scale production and application of these composite carbon sources?
Scalability challenges include consistent sourcing and pretreatment of agricultural residues, uniform blending with PHBV, and shaping into suitable forms (e.g., pellets, sheets) for reactor packing. The study used laboratory-scale preparation; industrial scale-up would require optimization of mixing and extrusion processes. Additionally, long-term performance in real wastewater matrices and reactor configurations needs validation.
How do the release kinetics of these composites affect denitrification rates in continuous-flow reactors?
The release kinetics, characterized by mass transfer coefficient k and maximum release M∞, directly influence carbon availability. Optimal composites like CC4 provide moderate release rates that match denitrification demand, avoiding excess carbon that could lead to secondary pollution. The study did not measure denitrification rates directly, but the enhanced bioavailability of released DOM suggests improved denitrification efficiency.
What is the environmental impact of residual PHBV and cellulose after carbon depletion?
PHBV is biodegradable, breaking down into CO2 and water under microbial action, while cellulose is also biodegradable. The study did not assess residual effects, but the use of biodegradable materials minimizes long-term environmental persistence. However, the release of DOM with lower aromaticity and molecular weight may be more readily assimilated, reducing potential for harmful byproducts.
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