On the paper trail: from sludge to soil

Waste paper sludge can be put to beneficial use in the agricultural sector to improve performance as Andrew Urquhart explains.

Waste sludge and crumb from the paper industry can be recycled in an effective manner if a number of key issues are addressed. First, the chemical, biological and physical properties of the waste are fit for end use purpose. Second, the financial, environmental and ecological merit of the proposed recycling activity. Third, sustainability - such as energy use, water use, pollution, and lastly, the potential local market for the sludge/crumb.

The Environmental Permitting Regulations (EPR) introduced last April apply to pulp and paper manufacturing activities where the plant has a production capacity of more than 20 tonnes per day. This covers any activity associated with making paper pulp or paper, including recycling.

The paper industry is highly proficient in the recycling of its products, but the number of times that cellulose fibres can be re-used is finite because the fibre length decreases with each use and the fibre strength decreases. At this point, the fibres become a waste and so the challenge is to avoid sending de-inked sludge to landfill.

Fibre recovery
The EPR states that operators should 'consider all avenues for recovery of fibre and filler from de-inking and wastewater treatment'. Several options exist, for example, incineration can be employed to generate energy. However, the EPR also allows 'landspreading, where it represents a genuine agricultural benefit or ecological improvement and the ultimate fate of pollutants present pose no environmental harm'.

Scientists from ADAS, the parent company of Envar, were part of the team that developed the safe sludge matrix that stipulates the suitability of biosolids being spread to land in relation to different crops. Further activity involving the application of waste materials to land includes the spreading of flocculent sludge from water treatment to agriculture and the utilisation of digestate from anaerobic digestion for the improvement of agricultural soils.

Envar works for a large number of paper mills including Severnside Recycling, which recovers around 1.9M tonnes of material annually. Together the two companies are tackling 26,000 tonnes of waste material that is generated by the St Regis' Hollins Mill in Darwen, Lancashire.

Envar's role in the partnership with Severnside has been to evaluate recycling options for the mill's paper sludge and crumb, and to ensure that the most sustainable option is adopted. A number of alternatives were considered, including incineration, land restoration, soil improvement and animal bedding. Of these, the latter three were considered to offer the greatest benefits.

Paper crumb
The paper crumb from the mill is ideal as a bedding product because it has a low moisture content and no odour, offering livestock farmers a cost-effective and sustainable alternative to intensively farmed straw. Furthermore, paper sludge contains useful plant nutrients and a high proportion of organic matter. It is also alkaline, which is beneficial to many agricultural soils.

Paper sludge can be used in restoration projects as an ingredient in manufactured soil. If trees are then grown on the site, these can be harvested at a later date for paper manufacture, offering a longer term closed loop recycling option. As Envar has a high level of engagement with the farming community, it can help secure local markets for the products of recycling, helping to reduce CO2 emissions in line with the sustainability objectives of all stakeholders.

Soil science also plays an important role when paper sludge is utilised on agricultural land. This is because the physical and chemical attributes of land has to be matched with the properties of the recycled material. This is important because the Environment Agency has to be satisfied that the requirements of the EPR are being met. Sludge recycling is therefore a very attractive proposition as long as it is managed in a responsible manner.

Andrew Urquhart is director of development at Envar

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