Biosolids and other bioresources have been safely and successfully applied to agricultural land for many years – and this market remains the best environmental option for these materials. Farmers benefit from reduced fertiliser bills and for bulky materials such as composts, biosolids cake and farmyard manures – soils benefit from increased organic matter. Data from field and desk studies continue to support the recycling of bioresources to agricultural land, but there are some aspects for which data are not yet available. This one day event considered this situation, with microplastics as an example. The question of plastics in the environment is of high public interest, and there are data showing the presence of microfibres and microplastics in bioresources and soils. Whether this presence is problematic is not known – but visible plastic contamination has already created market push-back against (food-based) digestates in Scotland. This issue was resolved through the voluntary adoption of very low plastic levels – well below those required in the compost (PAS100) and digestate (PAS110) certification schemes. These limits serve to manage perception, but are not based on empirical evidence. Despite this, SEPA have now incorporated them into regulation. The panel of expert speakers all agreed that regulatory approaches should be based on evidence, and that – pending any findings to the contrary – the practise of applying bioresources to agricultural land should continue. Whilst there are trace concentrations of many organic compounds in materials such as biosolids, direct-feeding trials with dairy cattle show no risk to animal or human health – but do raise questions around potential for future source controls of these compounds. Brominated flame retardants are increasingly common in the environment, through their use in furniture and soft furnishings – but it’s not clear that they are still necessary, as the behaviours that originally led to the introduction of these compounds (particularly smoking in the home) have changed, and both smoke and fire detection are now compulsory.
The water, waste and farming sectors also face other challenges – with the recent ‘Farming rules for water’ requiring the application of materials to meet agronomic demands. This will require investment in (for example) digestate storage, and may see future investment in practises such as slurry acidification – which help to ensure that agronomic nitrogen remains in the soil and available for crop uptake, rather than being lost to atmosphere. Predicting the crop availability of phosphates is not straightforward, and in contrast to spring application of nitrogenous fertilisers, biosolids and other phosphate sources may be best applied in the autumn. However, as climate change causes an increase in the intensity of rainfall events, any fertiliser application onto soils above field drains needs to be handled with care, to minimise risks of immediate run-off into water courses. Producers of bioresources can best ensure appropriate use of their materials by managing the spreading operations in-house, which also minimises costs. Such direct relationships also allow producers to respond immediately to any quality issues, retaining farmer confidence. Moving from free supply to a paying customer base is also possible, through careful brand positioning and the use of trusted advisers – and while some water companies are aiming higher than others, the benefits of audited quality schemes such as the BAS (Biosolids Assurance Scheme) are increasingly evident.
With today’s focus on soil quality, bioresources will play an important role in sustainable food production – their use supported by robust evidence and improved farmer engagement. By retaining a focus on quality and customer relationships, bioresource producers should retain access to agricultural landbank for the foreseeable future.