Each of us releases around 1.5 grammes of phosphorus per day into sewage[1], and sewage also contains phosphorus from food wastes, organic materials, detergents and industrial sources. Today, around one quarter of the phosphates in municipal sewage in Europe are already effectively recycled as fertiliser values to agriculture : 39-45% of phosphates in EU sewage are removed[2] and then 53% of sewage sludges are reused in agriculture[3].

National objectives

Both Germany and Sweden have announced national objectives for phosphorus recovery for recycling from sewage[4]. Sweden’s action plan centres on recycling P to land through sewage sludge use in farming, whereas the German Federal Environment Office (UBA) suggests recovery for recycling in sewage works. Phosphate recovery is now also officially included in UK Environment Agency strategy[5].

The German Federal Environment office announced in March 2003 the objective of developing phosphorus recovery for recycling from sewage and other wastes. The press release followed the organisation of a symposium (Berlin, 6-7 Feb. 2003) which brought together around one hundred German experts, regulators and water industry operators to discuss P-recovery from sewage and wastes. A paper presented by UBA at this conference suggests that existing taxes on waste water could be used to support the technical development of phosphorus recycling, and that P-recovery and recycling requirements could be instated within the terms of existing waste and water legislation.[6]

Sweden has also announced the objective of developing phosphorus recycling, but the Swedish action plan published in 2002[7] proposes to achieve 60% P-recycling by 2015 largely by re-use in agricultural by sewage sludge spreading. The Agency estimates that at present 46% of sewage phosphorus is already effectively recycled through agricultural sludge application. Sweden hopes to move back to agricultural sludge spreading by implementing sludge quality criteria which. The environmental courts in Sweden have already begun to condition operating authorisations for sewage sludge incineration on the implementation of phosphate recovery. The cities of Ekilstuna, Falun, Halmstad, Malmö, Södertälje and Stockhom are already subject to such a requirement, or the issue is now being addressed[8].

The European detergent industry has also fixed as an objective that 25% of detergent phosphates should come from recycling within a decade[9]. This places phosphates in a unique position as a potentially sustainable detergent component.

Phosphorus recycling

The application of the EU Urban Waste Water Treatment Directive 91/271 means that phosphates in domestic waste water, be they from detergents, food wastes or from natural bodily emissions (the main source) are effectively no longer an environmental issue. This Directive requires that phosphates be removed wherever sewage works situated in conurbations of more than 10,000 “person equivalent” (that is villages or groups of villages or more than around 6-7,000 population) discharge into surface waters which are susceptible or potentially susceptible to eutrophication. That is, phosphates must be removed from sewage wherever they are a potential environmental issue. These requirements are effectively confirmed and reinforced by the recent EU Water Framework Directive[10].

Where sewage sludges are spread on agricultural land, phosphates are already effectively recycled, as fertilisers contributing to crop growth. However, agricultural re-use of sewage sludge is diminishing throughout Europe, for a variety of reasons independent from phosphorus contents.

Agricultural re-use of sewage sludge is diminishing both for logistic, environmental and social reasons. Around big cities, there is simply not enough farmland available to spread sludge production. In other cases, spreading is limited by levels of contaminants in sewage sludge, in particular heavy metals. More generally, there is a tendency for farmers to refuse sewage sludge, often under pressure from supermarkets and food processing companies, in response to varying consumer concerns from hormones to pharmaceutical residues (even though there may be no rational basis for such perceived risks ).

Where sludges are no longer used on land, they will increasingly have to be treated by incineration or other thermal processes. This will mean that phosphates become a dead weight in the thermal treatment, and then finish their life in sludge incineration ash, consigned to landfill. Where sewage sludge is disposed of by use as an energy source in the cement industry, phosphates are not only a dead weight but even a problem, as they affect the setting properties of the cement.

Biomass production

Phosphorus can also be recycled from sewage by using it, either directly, or as sewage sludges, as a fertiliser and support for the growth of plants or biomass, which can then be used as animal feed, to produce compost, as an energy source, or as a raw material for industrial processes. Such systems can use sewage, and so recycle phosphorus and other nutrients, to produce algal or water plant biomass, wood or other energy crops, etc.

Phosphorus recovery

Phosphate recovery consists of extracting phosphates from the sewage works in a form which can be used either industrially (as a raw material in the phosphate industry) or as a fertiliser (either directly as recovered, or after further processing or mixing by the fertiliser industry). P-recovery is feasible, for example, by precipitation of calcium phosphates, struvite (MAP, magnesium ammonium phosphate) or potassium struvite (potassium ammonium phosphate, K-struvite).

Phosphorus recycling potentially offers economic returns through the commercial value of the recovered product, through economies in sludge management and improvements in sewage works operation.

Cost/benefits of phosphorus-recovery :

A number of full scale or pilot recovery installations are already operational in sewage works treatment centres in several countries, recovering phosphates as calcium phosphates (Geestmerambacht, The Netherlands), as struvite (Canada, UK, Italy, Japan …) or as potassium struvite from veal calf manures (Putten, The Netherlands).

The industrial use of recovered phosphates has been successfully tested and is operational at the Thermphos International plant, Vlissingen, The Netherlands (use as a secondary raw material of recovered calcium phosphates from Geestmerambacht sewage works since 1998, and currently testing of the use of sewage sludge incineration ashes from The Netherlands, Germany).

Fertiliser value

Struvite can be used directly as a fertiliser, or mixed with other compounds to provide specific fertiliser properties. Struvite produced by recovering phosphate is in some circumstances sold with an added marketing value as a “green recycled” product, as in the UK, Japan and recently Canada.

Market prices for the sale of such recovered struvite have been reported as:

• 464 €/tonne according to Schu et al., Australia, 2006 [11]
• 2,700 yen = 166 €/tonne gross sale price for sewage-recovered struvite reported in Japan, 2001.  The fertiliser, after mixing with other products to provide a potassium content, is then sold to the public for 1 – 2,000 yen (3,000 – 6,100 €) per 20kg bag. [12]
• UK£ 217 – 865 = 320 – 1290 € UK, 2000 [13]

Agronomic studies of the fertiliser value of struvite are summarised in SCOPE Newsletter n° 43 at www.ceep-phosphates.org and further recent trials of struvite as a fertiliser are summarised in Scope Newsletters n°s 69 (wheat), 68 (rye grass), 60 (field tests on potatoes[14]), 50 (oats and rye grass). These suggest that struvite is as good a phosphorus source as commercial fertilisers, comparable to Triple Super Phosphate and maybe better than DCP (Di Calcium Phosphate)

Working together

A number of international conferences have brought together R&D teams and scientists, water and animal waste industry (water companies, engineering companies) and regulators to exchange information about the different technical routes, economics and operational feasibility of phosphorus recovery.

Papers from these different conferences are available on this website, see under “Conference documents”.

Closing the loop

Phosphate recycling is essential for the sustainable future of our society as it is inconceivable to continue to simply throw away a non-renewable resource which is essential for life. Whilst this is a long term objective, increasing economic pressure on sewage sludge disposal and on water industry environmental life-cycle responsibility are likely to bring phosphate recycling into the short-term future.

The best way to recycle phosphorus is agricultural re-use of sewage solids, but problems with logistics (lack of farmland around big cities), contamination with pollutants and consumer resistance mean that this route is fast disappearing in many countries. In situations where agricultural re-use is not possible, industrial recycling of phosphates offers a sustainable solution. Phosphates from sewage (of human, food waste, detergent or industrial origin, recovered together) or from animal manures can be industrially recycled into either fertilisers or into industrial phosphate applications (flame retardants, detergents, electronics …).