Biosolids Digestion System with Acidic Hydrolysis Stage
Solution Overview
Problem
The disposal of biosolids from wastewater treatment is challenging due to the presence of pathogenic microorganisms, which pose health risks and are subject to legal restrictions, making it difficult to dispose of them safely and legally.
Innovation Solution
A multi-stage process involving acidic hydrolysis, anaerobic digestion, thermophilic aerobic digestion, and mesophilic digestion, along with a recycling system, is employed to treat biosolids. This process includes hydrolyzing insoluble organic polymers, fermenting volatile fatty acids, and transferring nitrates from mesophilic digestion to acidic hydrolysis environments to control pH and inhibit sulfate-reducing bacteria.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If biosolids are disposed of directly after wastewater treatment, then disposal is simple and quick, but pathogenic microorganisms pose health risks and legal restrictions prevent safe disposal
Solution Approach 1:
The digestion process is divided into multiple stages: hydrolysis stage, anaerobic digestion stage, and aerobic digestion stage. Each stage targets specific contaminants and occurs under different environmental conditions, systematically eliminating pathogenic microorganisms while preserving beneficial ones.
Solution Approach 2:
The process performs preliminary hydrolysis of insoluble organic polymers before anaerobic digestion, breaking down complex structures into simpler compounds that are easier to digest and less likely to contain pathogens. This preliminary action prepares the biosolids for more effective subsequent treatment.
2Object-affected harmful factors
If thermophilic digestion is used to kill pathogenic microorganisms, then pathogen inactivation is effective, but energy consumption increases due to high temperature maintenance
Solution Approach 1:
The system alternates between anaerobic and aerobic digestion periods, utilizing the heat generated during aerobic stages to maintain temperatures for pathogen inactivation without requiring continuous high-energy input. The periodic switching allows natural heat recovery and reduces overall energy consumption.
Solution Approach 2:
The aerobic digestion stage is designed to be autothermal, generating its own heat through microbial respiration and oxidation processes. This self-service capability eliminates the need for external heating systems, significantly reducing energy consumption while still achieving effective pathogen inactivation.
3Object-affected harmful factors
If multiple digestion stages are implemented to fully treat biosolids, then treatment effectiveness improves, but process complexity increases
Solution Approach 1:
Multiple digestion functions are combined into integrated reactors where hydrolysis, anaerobic digestion, and aerobic digestion occur in sequence within a unified system. The reactors are designed to be mutually supportive, with outputs from one stage serving as inputs for the next, reducing the need for separate isolated systems.
Solution Approach 2:
The digestion system is designed to handle multiple functions simultaneously: contaminant destruction, pathogen inactivation, biogas production, and nutrient recovery. The same microbial communities and reactor conditions support multiple objectives, making the system more efficient and less complex than separate specialized systems.
4Object-generated harmful factors
If nitrates are transferred from mesophilic digestion to acidic hydrolysis environment, then sulfate-reducing bacteria activity is inhibited, but additional transfer and control mechanisms are required
Solution Approach 1:
The system uses feedback control to monitor nitrate levels and sulfate-reducing bacteria activity, adjusting the recycle ratio and transfer timing to maintain optimal conditions. Sensors detect hydrogen sulfide production and automatically adjust process parameters to prevent sulfate-reducing bacteria from becoming active.
Solution Approach 2:
The mesophilic digestion reactor serves as an intermediary zone where nitrates are generated and stored before being transferred to the acidic hydrolysis environment. This intermediary function allows controlled release of nitrates, preventing direct contact between high nitrate concentrations and sulfate-reducing bacteria while still achieving effective inhibition.
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 effectively reduces the concentration of harmful byproducts, such as ammonia and hydrogen sulfide, and increases the production of biogas with high methane content, making it possible to safely dispose of treated biosolids and recover valuable resources.
Implementation Method 1
hydrolyzing insoluble organic polymers in a sludge derived from wastewater in an acidic hydrolysis environment having a pH between 5 and 6 to produce hydrolyzed biosolids
Implementation Method 2
fermenting the hydrolyzed biosolids in an anaerobic digestion environment to produce anaerobically digested biosolids and biogas
Implementation Method 3
digesting the anaerobically digested biosolids in a thermophilic aerobic digestion environment to produce thermophilically digested biosolids
Implementation Method 4
digesting the anaerobically digested biosolids or the thermophilically digested biosolids in a mesophilic digestion environment to produce mesophilically digested biosolids comprising nitrates
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Processes and system are provided for digesting biosolids in a multistage digestion system. The processes and system are well suited for producing Class A biosolids and biogas containing a high content of methane. Methods anti systems are also provided for recovery of phosphorus from wastewater and biosolids.