How can we recover ammonium and phosphate from biogas slurry?

Write in the journal Sustainability, a team of researchers investigated the recovery of ammonium and phosphate from biogas sludge, taking a multivariate statistical approach to the research question. Authors from China and Pakistan contributed to the research.

Study: Ammonium and phosphate recovery from biogas sludge: multivariate statistical analysis approach. Image Credit: NotionPic/Shutterstock.com

Nutrient recovery from livestock manure

Agriculture and animal husbandry have grown exponentially over the past century to meet the demands of a growing world population. Today, large industrialized farms are a common feature of many countries around the world. This growth has facilitated the need for biogas refineries to convert agricultural waste into value-added materials such as biogas slurry for use in fertilizers.

(a) Principal component analysis (PCA) of phosphate and ammonium concentration, and scavenging effect of different biochars;  (b) phosphate and ammonium concentration, and the removal effect of different pyrolysis temperatures;  (c) phosphate concentration in different elements;  (d) different phosphate removal;  (e) non-ammonium element concentration;  (f) elimination of the various ammonium elements.

(a) Principal component analysis (PCA) of phosphate and ammonium concentration, and scavenging effect of different biochars;  (b) phosphate and ammonium concentration, and the removal effect of different pyrolysis temperatures;  (c) phosphate concentration in different elements;  (d) different phosphate removal;  (e) non-ammonium element concentration;  (f) elimination of the various ammonium elements.

(a) Principal component analysis (PCA) of phosphate and ammonium concentration, and scavenging effect of different biochars;  (b) phosphate and ammonium concentration, and the removal effect of different pyrolysis temperatures;  (c) phosphate concentration in different elements;  (d) different phosphate removal;  (e) non-ammonium element concentration;  (f) elimination of the various ammonium elements.

(a) Principal component analysis (PCA) of phosphate and ammonium concentration, and scavenging effect of different biochars;  (b) phosphate and ammonium concentration, and the removal effect of different pyrolysis temperatures;  (c) phosphate concentration in different elements;  (d) different phosphate removal;  (e) non-ammonium element concentration;  (f) elimination of the various ammonium elements.

(a) Principal component analysis (PCA) of phosphate and ammonium concentration, and the removal effect of different biochars; (b) phosphate and ammonium concentration, and removal effect of different pyrolysis temperatures; (vs) concentration of different phosphate elements; (D) different elimination of phosphates; (and) different concentration of ammonium element; (F) elimination of the various ammonium elements. Image Credit: sustainability

This organic matter is suitable for this purpose due to the large amount of bioavailable nutrients, such as potassium, phosphorus, nitrogen and carbon. However, this organic matter has insufficient value-added properties, hampering its widespread agricultural use compared to solid fertilizers. In addition, excessive slurry production presents environmental problems such as water and air pollution.

In many countries, slurry handling is a critical issue in the agricultural industry. However, agriculturally important chemicals such as nitrogen and phosphate in slurry can be recovered, which offers great potential for improving the circularity of the agricultural industry. Several techniques can be used for this purpose, including plant absorption, adsorbents and membrane filtration.

However, several methods have drawbacks. For example, membrane clogging and contamination can occur in membrane filtration methods. Using plants to take up nutrients requires a large use of land due to the low value-added qualities of slurry. Adsorbents offer an economical, energy-efficient and simple alternative. They can remove environmental pollutants and can be used as soil amendments and fertilizers.

(a) Relationship between ammonium concentration and ammonium removal efficiency under different elemental concentrations, (b) phosphate concentration with phosphate removal efficiency under the effect of biochar;  (c) ammonium concentration with ammonium removal efficiency at the pyrolysis temperature;  (d) phosphate concentration with phosphate removal efficiency at pyrolysis temperature;  (e) ammonium concentration with ammonium removal efficiency under different elemental concentrations;  (f) Phosphate concentration with phosphate removal efficiency under different elemental concentrations.  The number of repetitions is (n = 3).

(a) Relationship between ammonium concentration and ammonium removal efficiency under different elemental concentrations, (b) phosphate concentration with phosphate removal efficiency under the effect of biochar; (vs) ammonium concentration with ammonium removal efficiency at pyrolysis temperature; (D) phosphate concentration with phosphate removal efficiency at pyrolysis temperature; (and) ammonium concentration with ammonium removal efficiency under different elemental concentrations; (F) phosphate concentration with phosphate removal efficiency under different elemental concentrations. The number of repetitions is (n = 3). Image Credit: sustainability

Improve nutrient recovery efficiency

Struvite contains high levels of phosphates and nitrogen and is an effective slow-release fertilizer, meaning nutrients are available to crops for longer periods of time, requiring less land and fertilizer to deliver as much nutrients to plants than conventional fertilizers. Recovering these nutrients from slurry by struvite crystallization is a simple, fast and cost-effective strategy.

Biochar is a good adsorbent to recover nutrients. Pyrolysis of organic matter produces solid matter that contains high levels of carbon and other nutrients found in biomass. According to some studies, the generation of biochar biomass contaminated with metal ions can recover phosphates.

Another problem in the environmental remediation of agricultural wastes is the proliferation of phosphates and nitrogen-containing chemicals such as ammonium from sewage, where they can cause problems such as pollution and the proliferation of algae. Several techniques have been explored, but the need for an effective method to remove these contaminants before they cause damage to marine ecosystems is crucial.

Removing these agriculturally important and environmentally critical nutrients from the environment is a major challenge for environmental scientists. Their recovery from slurry and biochar could prove very beneficial for both the agricultural industry and the field of environmental remediation.

The study

The article formulated two main hypotheses. First, the authors hypothesized that the recovery of ammonium and phosphate from slurry using the co-precipitation of biochar and struvite might be a viable strategy to remove and utilize these contaminants. for value-added products. Second, they hypothesized that multivariate statistical analysis might be appropriate to elucidate the correlation between recovered ammonium and phosphate and quality indicators.

The main route of elimination is the main: (a) elimination of phosphates, (b) elimination of ammonium.

The main path for removing the main route: (a) elimination of phosphates, (b) elimination of ammonium. Image Credit: sustainability

In doing so, the authors stated that it is possible to effectively use trajectory analysis, regression, principal component and Pearson correlations to provide accurate information on the recovery of ammonium and phosphate from slurry. Several inorganic salts were evaluated in the study.

The results of the study indicate that as an adsorbent, struvite performs best. Its performance on mushroom soils and rice biochar was evaluated, demonstrating superior ammonium and phosphate recovery. California2+ the impact on struvite formation has been reduced. A substantial nutrient recovery effect was observed, with 99% phosphate and 71% ammonium recovered under optimum conditions.

With respect to multivariate analysis, a Pearson correlation was found to be largely insignificant in many ion concentrations evaluated. All indicators in the combined multivariate analysis had a positive or negative effect on each other. Additionally, it has been found that parameters such as pH, temperature, and concentrations of various chemical components influence the recovery of ammonium and phosphate.

In summary, this research uncovered the methods that govern the efficient reuse of nutrients in slurry by biochar. The results indicated that mushroom soil and rice biochar could be used as efficient nitrogen and phosphate binders for nutrient recovery and could be used as slow-release fertilizer. Additionally, the authors stated that the research provides benefits for biogas sludge disposal in both rural and urban areas.

Further reading

Kubar, AA et al. (2022) Ammonium and Phosphate Recovery from Biogas Sludge: Multivariate Statistical Analysis Approach Sustainability 14(9) 5617 [online] mdpi.com. Available at: https://www.mdpi.com/2071-1050/14/9/5617

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