Pilot-Scale Direct Filtration of Bullfrog Farming Wastewater

Pilot-Scale Summary Report on the Treatment of Bullfrog Farming Wastewater Using Three-None Direct Filtration Technology

Project Name: Pilot-Scale Direct Filtration Trial of Bullfrog Farming Wastewater

Pilot-scale testing period: November 1, 2023 – December 31, 2023

Pilot-scale testing site: XX Bullfrog Farming Base, Huizhou City

Report Prepared by: Myfuter Water (Guangdong) Co., Ltd.

I. Project Background

Frog farming is characterized by high stocking density, intensive feeding, and substantial excretion. The resulting aquaculture effluent primarily consists of uneaten feed, feces, suspended solids, and nitrogen- and phosphorus-containing organic matter, exhibiting high chemical oxygen demand (COD), high suspended solids concentration, and significant water-quality fluctuations. Conventional pretreatment processes—such as sedimentation, dissolved-air flotation, and biological treatment—suffer from drawbacks including large land footprint, high chemical consumption, and complex operation and maintenance, making it difficult for them to keep pace with the increasingly stringent discharge standards for aquaculture effluent.

To explore efficient, low-carbon, and intensive pretreatment technologies for aquaculture wastewater, this pilot-scale study employed a “three-no” direct filtration process—requiring no external power, no consumables, and no pre-treatment of influent quality—to directly filter bullfrog farming wastewater. The performance of this approach in terms of suspended solids removal, pollutant reduction, and operational stability was evaluated to provide a scientific basis for subsequent full-scale engineering applications.

II. Pilot-Scale Testing Objectives

1. Evaluate the removal efficiency of the “three-no” direct filtration system for suspended solids (SS), chemical oxygen demand (COD), total phosphorus (TP), and total nitrogen (TN) in bullfrog aquaculture wastewater.

2. Evaluate the system’s operational stability and shock resistance under conditions with no chemical dosing or with only trace amounts of chemicals;

3. Evaluate the system’s operating costs (electricity consumption, chemical consumption, and maintenance) as well as the characteristics of sludge production;

4. Provide design parameters and operational recommendations for subsequent large-scale applications.

III. Overview of the Pilot Test

3.1 Test Site and Wastewater Sources

The pilot-scale testing was conducted at the XX Bullfrog Farm in Huizhou. The wastewater sample was collected from the effluent channel of the aquaculture ponds, exhibiting significant fluctuations in water quality and typical characteristics of high-concentration aquaculture wastewater.

3.2 Test Equipment

A skid-mounted, integrated three-in-one direct filtration system is employed, with a design treatment capacity of 2–3 m³/h. The core filtration unit consists of an anti-fouling ASSFBR filter cartridge assembly and is equipped with an automatic backwash system, enabling continuous operation.

3.3 Test Plan

Pilot-scale testing is divided into three phases:

3.4 Raw Water Quality

IV. Pilot-Scale Test Results and Analysis  

4.1 Suspended Solids (SS) Removal Efficiency

Analysis: Under no-chemical conditions, the SS removal rate remains stable at above 80%; upon addition of a trace amount of PAC, the removal rate increases to over 96%, with the effluent SS consistently below 20 mg/L, thereby meeting the influent requirements for subsequent biochemical treatment.

4.2 Organic Matter (COD) Removal Efficiency

Analysis: The three-no direct filtration exhibits limited removal of dissolved COD but effectively retains suspended and colloidal COD. During stages two and three, the COD removal rate remains stable at above 55%, significantly reducing the organic load on the subsequent biochemical treatment system.

4.3 Total Phosphorus (TP) Removal Efficiency

Analysis: In bullfrog aquaculture wastewater, phosphorus primarily exists in particulate form. During Phase 1, physical filtration alone achieves some removal of particulate phosphorus; in Phase 2, the addition of PAC significantly enhances total phosphorus (TP) removal through flocculation, stabilizing it at above 95%.

4.4 Ammonia Nitrogen (NH₃-N) and Total Nitrogen (TN) Removal Efficiency

Analysis: The three-no direct filtration process does not directly remove dissolved ammoniacal nitrogen, but it does retain a certain amount of suspended organic nitrogen, resulting in a moderate reduction in total nitrogen. Removal of ammoniacal nitrogen relies on subsequent biochemical treatment.

4.5 Turbidity and Color

· Phase 1: Average turbidity of the produced water is 32 NTU, with a noticeable reduction in color.

· Phase 2/3: Average turbidity of the produced water is 6.5 NTU, with clear and transparent water quality and near-complete removal of color.

4.6 Operational Stability and Shock Resistance

During the pilot-scale trial, the system operated continuously for 60 days, enduring multiple fluctuations in influent water quality (with instantaneous SS peaks reaching 400 mg/L), yet the effluent quality remained stable, with no clogging or sudden flux decline observed. The automated backwashing system functioned properly, requiring extremely infrequent maintenance.

V. Sludge Generation and Disposal

Conclusion: Sludge with low moisture content and reduced volume can be directly dewatered and pressed for use as organic fertilizer feedstock or transported off-site for disposal, achieving approximately 50% sludge reduction compared with conventional dissolved air flotation.

VI. Operating Cost Accounting

Compared with the conventional air flotation–sedimentation process (with an operating cost of approximately RMB 1.5–2.5 per ton of water), the operating cost is reduced by more than 65%.

VII. Pilot-Scale Test Conclusions

1. Significant treatment performance: The “three-no” direct filtration technology achieves stable SS removal rates of ≥95%, TP removal rates of ≥95%, and COD removal rates of ≥55% in bullfrog aquaculture wastewater, with effluent turbidity ≤8 NTU, thereby providing high-quality influent conditions for subsequent biochemical treatment.

2. Stable and reliable operation: The system exhibits strong shock resistance, effectively accommodating the wide fluctuations in the quality of bullfrog aquaculture wastewater. During continuous operation, it experiences no clogging or flux decline, and its automated operation and maintenance are straightforward.

3. Outstanding economic advantages: the comprehensive operating cost is approximately RMB 0.7 per ton of water, representing a reduction of more than 65% compared with conventional processes; sludge volume is reduced by 50%, leading to a substantial decrease in disposal costs.

4. Resource Recovery Potential: The intercepted solid sludge consists primarily of leftover feed and feces, with no residual chemical additives, making it suitable as a raw material for organic fertilizer and enabling resource recovery.

5. Engineering Promotion Value: Integrated skid-mounted equipment occupies a small footprint and is highly mobile, making it well suited for new construction or retrofit projects at decentralized bullfrog farms.

VIII. Follow-up Recommendations

1. Conduct scaled-up pilot testing: It is recommended to validate the process at a larger scale (10–50 m³/d) and further optimize the operating parameters.

2. Integrated biochemical treatment process: Explore a combined process of “three-no direct filtration plus high-efficiency biochemical treatment (such as MBR and contact oxidation)” to achieve stable compliance with discharge standards for aquaculture effluent.

3. Exploration of Resource Recovery Pathways: Conduct compositional analysis and resource recovery trials on the intercepted solid residues to develop applications in organic fertilizer production or anaerobic digestion.

Report Prepared by: Myfuter Water (Guangdong) Co., Ltd.

Date: January 15, 2024

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