Biological Sludge Granulation via Acid-Oxidation Rotary Reactor
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Solution Overview
Problem
Biological sludge from wastewater purification processes poses challenges due to high moisture content, strong odors, and potential pathogenic bacteria, limiting its reuse as a fertilizer for agricultural soils, and existing treatment methods do not effectively address these issues.
Innovation Solution
A treatment process involving acid conditioning with sulphuric acid, followed by hydrogen peroxide treatment, and subsequent mixing with calcium oxide in a rotary reactor to produce a granular fertilizer with reduced moisture and sanitized properties, suitable for alkaline and saline soils.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If biological sludge is used directly as fertilizer, then organic substance and nutrients are provided to soil, but high moisture content makes management uneconomical and favors mineral fertilizers
Solution Approach 1:
The patent applies parameter changes by transforming the physical state of biological sludge from liquid/semi-solid to granular solid through a multi-step process involving acid conditioning, oxidation, alkaline treatment, and granulation. This changes moisture content from >60% to <30%, transforming it into a manageable fertilizer form while preserving organic substance and nutrients
2Quantity of substance
If biological sludge is used directly as fertilizer, then nutrients are provided to soil, but strong odors from anaerobiosis make handling and storage difficult
Solution Approach 1:
The patent converts the harmful anaerobic decomposition process that produces odorous gases into a beneficial controlled oxidation process. By adding hydrogen peroxide and maintaining aerobic conditions, the sludge is oxidized in a controlled manner that eliminates mercaptans, amines, and hydrogen sulphide while preserving nutrients, transforming the odor problem into a solution
Solution Approach 2:
The patent uses hydrogen peroxide as a strong oxidant to accelerate the oxidation of organic matter in biological sludge. This rapid oxidation prevents anaerobic decomposition and the formation of odorous compounds, while simultaneously sanitizing the sludge by destroying pathogenic bacteria and converting nutrients into plant-available forms
3Quantity of substance
If biological sludge is used directly as fertilizer, then organic substance is provided to soil, but pathogenic bacteria require sanitization treatments
Solution Approach 1:
The patent employs hydrogen peroxide as a powerful oxidizing agent that sanitizes biological sludge by destroying pathogenic bacteria, viruses, and other harmful microorganisms. The oxidation process breaks down cell walls and cellular structures of pathogens while preserving beneficial organic matter and nutrients, achieving both sanitation and nutrient retention in a single step
4Quantity of substance
If dehydrated residual sludge is produced, then moisture content is reduced, but semi-solid consistency does not allow easy management
Solution Approach 1:
The patent transforms dehydrated sludge from an irregular semi-solid mass into spherical granules with uniform size and shape. This granulation process, achieved through controlled aggregation and rolling in the rotary reactor, creates free-flowing particles that are easy to handle, transport, and apply, while maintaining high dry matter content and nutrient concentration
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The process results in a dried, granular fertilizer with high calcium and sulfur content, effectively addressing the challenges of moisture, odor, and pathogenic concerns, producing a product that is easily marketable and usable on agricultural soils, while integrating with wastewater purification plants to eliminate waste disposal issues.
Implementation Method 1
mixing means configured to mix the starting biological sludge with the sulphuric acid so as to perform an acid conditioning of the starting biological sludge
Implementation Method 2
the mixing reactor mixes the fluid acid sludge with the hydrogen peroxide solution
Implementation Method 3
mixing means configured to mix the starting biological sludge with the sulphuric acid so as to perform an acid conditioning of the starting biological sludge resulting in a fluid acid sludge with a temperature higher than and viscosity less than the starting biological sludge
Implementation Method 4
mixing system connected to means for feeding calcium oxide in powder form and configured to mix thoroughly the fluid acid sludge extracted from the at least one batch mixing reactor and the calcium oxide in powder form and to output an alkaline mixture
Implementation Method 5
during transit of the mixture from the upstream inlet to the downstream outlet, a temperature of the mixture inside the reaction chamber exceeds 90°C and the mixture is dehydrated with the production of steam
Implementation Method 6
a temperature of the mixture inside the reaction chamber exceeds 90°C
Implementation Method 7
providing at the downstream outlet a dried resulting material which is a granular fertilizer (MBR3) in the form of granules
Data Source
Figure 1
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Figure 3~4
AI summary
Process for treating starting biological sludge (MBR0) with a dry fraction and a liquid fraction, wherein the dry fraction is greater than or equal to 15% by weight of the starting biological sludge, comprising: acid conditioning of the starting biological sludge (MBR0) by means of mixing with sulphuric acid, resulting in a fluid acid sludge with a temperature higher than and viscosity less than the starting biological sludge; oxidising treatment of the fluid acid sludge by means of mixing with a hydrogen peroxide solution; mixing of the fluid acid sludge (MBR1) resulting from the oxidising treatment with calcium oxide in powder form, resulting in an alkaline mixture (MBR2) comprising hydrolysed organic material and calcium sulphate; feeding of the mixture (MBR2) comprising hydrolysed organic material and calcium sulphate inside a rotary reactor (10) with a reaction chamber (100) extending between an upstream inlet for feeding the mixture and a downstream outlet, further comprising an upstream opening (11) for outputting gaseous substances; rotating the rotary reactor (10) so that the mixture (MBR2) is mixed and turned around and moves from the upstream inlet to the downstream outlet in the reaction chamber (100). During the rotation of the rotary reactor (10) and the transit inside the reactor of the alkaline mixture (MBR2) from the upstream inlet to the downstream outlet, a temperature of the mixture inside the reaction chamber (100) exceeds 90°C and the mixture is dehydrated with steam production and an increase in the percentage of dry substance of the mixture to more than 55%, forming a dried surplus material which is a granular fertilizer (MBR3) in the form of granules with a residual moisture less than or equal to 40%, preferably of between 10% and 30%, suitable for use as a corrective for alkaline and/or saline agricultural soils. The granular fertilizer (MBR3) is then extracted from the downstream outlet of the rotary reactor.