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An important requirement of paper recycling is economical management of the residuals (a.k.a. sludge) of that activity. Pulping of newsprint and other recycled papers generates a residue which amounts to as much as one-third of the paper processed. Chemical properties of this material are essentially that of the recycled paper. The cost of disposition of this fibrous residue can impact the economic return on the recycling business.

Landfilling and land application of paper mill residuals have been the traditional management practice. However, the materials have been composted and the compost used for various horticultural purposes. The question we asked was could the residuals be used as an amendment alone or to supplement other amendments for composting biosolids.

The relatively high C:N ratio of about 100 and the fibrous physical property are definitely positive attributes. On the other hand, the residuals generally possess less than 50% dry solids and provide little porosity, definite disadvantages.

The purpose of this two phase study was to evaluate the paper recycling residuals as a supplement to or replacement for the dry shredded pallets and other clean woody wastes ordinarily used as an amendment in the biosolids co-composting facility. The study was conducted at the agitated bed, mechanically aerated Burlington County, NJ, Co-composting facility.

In Phase 1, four pilot scale mix ratios of biosolids, shredded woody waste, and paper recycling residuals were prepared. The proportion by volume consisting of paper residuals (CWF) bracketed the range from none to 100% of the amendment in the feedstock. At the conclusion of Phase 1 of this study, the operational staff recommended use of the paper recycling residuals at 100% of the amendment.

The mix (blended feedstock) used in Phase 2 possessed just 31% dry solids. This low percent solids would never be recommended where shredded wood was used as the sole amendment because of the stickiness, low porosity, and viscosity of the mix. The CWF proportion was used in Phase 2 only because of the surprising success observed in Phase 1. The high proportion of biosolids in the mix yielded a nitrogen-rich mix with nearly 3% TKN, and a C:N of 15. The VS content was 78%.

The compost prepared from biosolids – paper recycling residuals possessed higher concentrations of ammonia during the composting process and in the final product than the wood based compost. It was not clear whether this was due to lower porosity, less bioavailable carbon, or simply a lower C:N ratio of the input mix. The physical quality of the compost prepared with the residuals - biosolids mix was substantially different from that manufactured with shredded woody materials and biosolids. The compost consisted of grayish black fibrous balls 3 to 5 mm in diameter, relative to the shredded wood compost which consisted of brownish black woody chunks 5 to 20 mm long by 3 to 5 mm diameter. The economics of use of the residuals was evaluated (in part) based on tip fees received for biosolids and residuals, and the cost of supplying woody amendment. Based on just these three items, data suggested that when the cost of supplying woody amendment exceeds 9 per ton, paper recycling residuals can be used as an amendment without reducing the cash flow for operations.
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Document Type: Research Article

Publication date: 2004-01-01

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