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LOCAL RESEARCH: Composting of Municipal Sludge – Riverhead Wastewater Treatment Facility

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Executive Summary

A significant amount of biosolids is generated by the Riverhead Wastewater Treatment Facility (RHWTF) every year. Although biosolids have the potential to be transformed into compost through the composting process, the usual practice is to dispose them into landfills. Composting helps stabilize the organic matter in the biosolids (Oleszczuk, 2008), and the heat generated during the thermophilic phase also kills pathogens. The organic content of the sludge will be converted into stabilized humic substances through mineralization and, hence, the volume of the sludge is significantly reduced (Gouxue et al., 2001). These composted biosolids, once applied to the soil, can accelerate plant growth, improve soil moisture retention, increase organic matter in the soil, and control erosion of the topsoil (Liang et al., 2003). Since the RHWTF-generated biosolids have a very low carbon to nitrogen (C/N) ratio (8:1), they are usually landfilled. The fly ash (FA) generated from Corner Brook Pulp and Paper (CBPP), however, has a high carbon content; its addition to biosolids could increase the C/N ratio of biosolids. Therefore, the main objective of this study is to investigate the potential application of locally available carbonenriched ash from CBPP in improving the quality of biosolids generated by RHWTF, which serves the City of St. John’s, Mount Pearl, and Paradise.

Two parallel experiments were conducted under the same conditions: CBPP fly ash (CBPP FA) was added to one reactor; the other, without CBPP FA, was used as a control unit. The results of
these two reactors can be compared to determine the capability of wood ash as a stabilizer. Seven kilograms of digested wastewater sludge was weighed and added to both reactors, and two kilograms of fish waste processed in a food processer was also added to both reactors. An additional 500 grams of CBPP FA was added to one reactor. The samples were turned twice a
day to keep air flow of systems. The samples of 30 grams each were taken every three days over a 30-day period.

The C/N ratio and germination index (GI) are two parameters used to evaluate the stability and maturity of a compost. From the results of C/N ratio, it is clear that the addition of fly ash can significantly increase the C/N ratio. However, the C/N ratios for two types of compost over a 30-day period have similar trends and slopes, which indicates that adding fly ash may not accelerate the composting processes. Both of the two types of compost materials have a slight C/N ratio change, indicating that the composting of each is quite slow.

The GI results reveal that both composts are not adequately mature. Extending composting time is necessary. Compared with biosolids-only compost, the addition of fly ash hinders seed
germination. Therefore, a further study is suggested to investigate the phytotoxic compounds in the fly ash.


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