Sewage sludge as a sustainable fertilizer


by Hedwig Ens,

Ever thought of putting sewage on your plants? Scientists say thermally conditioned sewage sludge serves as an excellent fertilizer to improve soil properties. This was recently published in the open-access journal Frontiers in Nutrition. The major advantage over commercial fertilizers? Sustainable re-use of essential and finite phosphorus resources.

Phosphorus is a key nutrient for all living beings. When deficient in the diet, it severely compromises human health, and when deficient in agriculture, it restricts crop productivity. Without phosphorus, there can be no food production.

As the source of phosphorus is non-renewable phosphate rocks, there is a strong need for increased recycling to ensure phosphorus security. Efficient use and reduced environmental dissemination of phosphorus throughout the food system is needed to secure the ability to feed a growing global population.

As technological improvements increased the phosphorus content of sewage sludge, it now is a readily available alternative to commercial fertilizers in agriculture. To assess its effectiveness, Andry Andriamananjara from the University of Antananarivo (Madagascar) and his colleagues used a phosphorus radiotracer technique to measure the availability of phosphorus for plants in thermally conditioned sewage sludge.

They grew ryegrass in pots filled with soil that underwent isotopic P-labelling, and added either no fertilizer, thermally conditioned sewage sludge as fertilizer, or commercial triple superphosphate fertilizer. Shoot and roots were harvested at fixed intervals, and their radioactivity was analyzed to measure phosphorus uptake.

As expected, fertilizer application increased shoot biomass significantly over the harvest time, while only a trend towards an increase in root biomass was found. The addition of fertilizer increased phosphorus uptake by the plants. This wasn’t only because the fertilizer offered an additional phosphorus source, but also because the plants increased their soil exploitation.

However, total phosphorus uptake from thermally conditioned sewage sludge was lower than that from the commercial fertilizer. This could be explained by the fact that the phosphorus in the water-soluble commercial fertilizer is immediately available for plant uptake after application, whereas the phosphorus in thermally conditioned sewage sludge is present in a lower available form. Moreover, the other nutrients present in the sludge stimulated the microbial activity, thereby inducing competition between microorganisms and the plant roots for phosphorus uptake.

Dr. Andriamananjara would still recommend the usage of sewage sludge as fertilizer. He said: “It was shown to have a higher agronomic effectiveness in comparison with commercial fertilizer. Although on the short term it enhanced the microbial biomass and therefore phosphorus immobilization, on the longer term the phosphorus captured by this microbial biomass can again become available for the plants. Moreover, sewage sludge is a non-limited continuously available and sustainable fertilizer source.”

This research was published in the Research Topic Sustainable Phosphorus. This Topic gather papers covering the various issues regarding the efficient and sustainable use of phosphorus resources at a range of scales: from local to global, from agriculture to waste management.

Read the full article in Frontiers in Nutrition.

REPUBLISHING GUIDELINES: At Frontiers, open access and sharing research is part of our mission. Unless otherwise noted, you can republish our articles posted in the Frontiers blog – as long as you credit us with a link back.  Editing the articles or selling them is not allowed.

5 Comments on Sewage sludge as a sustainable fertilizer

  1. Treated sewage sludge is not a fertilizer. Nor is spreading this contaminated waste on land where we grow our food and forage a sustainable practice. Those entities profiting from this harmful practice depend on narrowly scoped nutrient research–such as the one cited in this blog– preferably done in greenhouses rather than in a more realistic environment to support their claim that land applied sludge is beneficial, sustainable, and safe. They ignore that every entity connected to a sewage treatment plant can legally pipe its hazardous chemical compounds into these facilities. We are not talking about just the emerging pollutants of concern, but about hundreds of long-recognized carcinogens, mutagens, neurotoxins like mercury, lead, arsenic, PCBs, dioxins, and pesticides which current sludge regulations either do not regulate, or regulate inadequately. These include synthetic chemical compounds for which we do not even have basic toxicity data, much less information about how they act synergistically in complex mixtures. There are over 90,000 of these compounds in commerce today, with 1000 new ones added annually. Most adhere to the solids when sewage is treated. Add to this super bugs which evolve when sewage is processed, which makes biosolids generated in our industrialized urban centers the most pollutant-rich waste mixture of the 21st century.

    Over a hundred health, farm, and environmental organizations–- many concerned with sustainable farming practices–-oppose growing food and forage on biosolids-treated land. Among them are the Sierra Club, the Natural Resources Defense Council, the Rodale Institute, the Institute for Agriculture and Trade Policy, Western Growers, the National Farmers Union, The Food Rights Network, and the Organic Consumers Association. All of these organizations depend on impartial scientific information to form their policy position.

  2. As usual Dr. Andriamananjara leaves out the risk factor:

    Try reading a little know regulation 40 CFR 261.30(d) and 261.33 (4), every US industry connected to a sewer can discharge any amount of hazardous and acute hazardous waste into sewage treatment plants.
    When the sewage industry tells you “pre-treatment of these industrial chemical are strictly regulated”, read the EPA’s Office of Inspector General’s Report No.14-P-0363- 09/2014 where you will instantly see they are BALD FACE PREVARICATORS! (Just Google the Report number).
    Now tell me what happens to those persistent hazardous chemicals when you heat them up and mix ALL of them together in a digester and send them out to a farm, forest or even in consumer product bags only labeled made from “bio solid.” By the way, The Texas Office of State Chemist (Texas A&M) is responsible for monitoring consumer bags of processed sewage sludge and have refused to analyze chemicals in these bags. I have the documentation on this.
    Chemicals that are persistent in the environment, bio-accumulate in people and/or wildlife, and are toxic are called PBTs. Because of these features, as long as they remain in commerce and may therefore be released into the environment, they will threaten the health of humans and wildlife.
    Farmers and Consumers are being badly used to dump municipal industrial, hospital, storm and household sewage on their farms to save cities money because of the cost to put it in a land fill.

  3. Jasdeep Singh Bhattal // August 17, 2016 at 7:34 pm // Reply

    This is very true, I’m a farmer and as well as Sewerage Engineer for last 35 years. The chemical fertilizers are quick where as application of sewerage sludge gives good results for many years.

  4. larry edwards // March 16, 2017 at 3:03 pm // Reply

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  5. Excellent article helpful us thats improve the production of crops thanks to sharing this kind of information.

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