Research on Technical Solutions for Restoring the Treatment Capacity of a Resort Wastewater Treatment Station
The wastewater treatment station is a crucial environmental facility for a resort, playing a pivotal role in its normal operation. Due to high visitor traffic and diverse service activities at resorts, wastewater quality fluctuates significantly. In particular, laundry wastewater often exhibits strong acidity, severely impacting subsequent biological treatment processes. This not only increases the difficulty of wastewater treatment but also elevates environmental risks. Currently, a resort's wastewater treatment station faces the challenge of treating approximately 400 m³/d of combined wastewater. Although the process design is reasonable, limited tank capacity and influent quality/quantity fluctuations exceeding the treatment capacity result in a particularly short hydraulic retention time (HRT) in the aerobic treatment stage, thereby affecting overall treatment efficiency. Consequently, how to enhance the treatment efficiency and effluent quality of the resort's wastewater treatment station through a series of technical and management improvements without constructing new tanks has become an urgent issue for the resort.
1. Project Overview
1.1 Treatment Capacity
Based on available technical data, combined with site surveys and communication, the combined wastewater flow of the resort's wastewater treatment station is determined to be approximately 400 m³/d.
1.2 Types of Wastewater Entering the Treatment Station
Currently, wastewater entering the resort's treatment station can be categorized by quality into three types: kitchen washing wastewater, laundry (linen) washing wastewater, and daily domestic sewage.
1.2.1 Kitchen Washing Wastewater
Kitchen washing wastewater contains grease and anionic surfactants (Linear Alkylbenzene Sulfonates, LAS).
1.2.2 Laundry (Linen) Washing Wastewater
Laundry washing wastewater may be acidic or alkaline, or possess strong oxidizing properties. It contains anionic/cationic surfactants, and its quality can vary significantly due to changes in detergent dosage, greatly impacting subsequent biological treatment.
1.2.3 Daily Domestic Sewage
The quality characteristics of domestic sewage from hotel guest rooms are similar to general domestic sewage.
1.3 Wastewater Quality Data
To renovate the resort's wastewater treatment station and restore its treatment capacity, samples of kitchen washing wastewater, laundry washing wastewater, and daily domestic sewage entering the station were collected before the renovation and sent to a certified testing company (CMA-accredited) for analysis. The test results for the relevant water samples are shown in Table 1.
1.4 Effluent Discharge Limit Requirements
The effluent from the resort's wastewater treatment station must comply with the primary standard (second period) values specified in *"Water Pollutant Discharge Limits" (DB 44/26-2001)*. Specific indicators are detailed in Table 2.
2. Analysis of Current Operation of the Treatment Station's Process
The current treatment process at the resort's wastewater treatment station consists of primary treatment using a screen well + equalization tank, and secondary treatment using an Anoxic-Oxic (AO) process (without nitrified liquor recycle). Treated effluent is discharged after disinfection, and surplus sludge is dewatered using a plate-and-frame filter press before off-site disposal, as shown in Figure 1. Therefore, the treatment station's process design is reasonable and possesses the capability to remove characteristic pollutants. The presence of an equalization tank allows for regulation of influent quality and quantity, pH neutralization, and adjustment of strong oxidizing properties. The biological treatment stage is configured as A-O-O, and through sludge recycle, it possesses a certain capability for simultaneous nitrogen and phosphorus removal. However, due to limited tank capacity, the operation of the resort's wastewater treatment station faces numerous issues.
2.1 Overloaded Operation Leading to Difficulties in Meeting Discharge Standards
Due to current influent quality and quantity exceeding the treatment station's capacity, and based on site surveys and communication, the estimated total HRT for the biological treatment stage + solids separation stage is only 6 hours. The influent COD concentration is as high as 856 mg/L, indicating that the station is currently overloaded, making it difficult for the effluent to meet discharge standards.
2.2 Fluctuations in Influent Quality, Quantity, pH, and Strong Oxidizing Properties
The influent to the resort's wastewater treatment station exhibits fluctuations in quality (COD), quantity (Q), pH, and strong oxidizing properties (NaClO, H₂O₂). Therefore, it is necessary to implement regulation of quality, quantity, pH, and adjustment of strong oxidizing properties to ensure the stable operation of subsequent biological treatment processes.
2.3 Aging Equipment Reducing Treatment Efficiency
The resort's wastewater treatment station suffers from aging equipment, further reducing treatment efficiency. Site surveys revealed violent turbulence in the aerobic tank with no visible fine bubbles, indicating potential rupture or failure of the fine-bubble diffusers at the tank bottom. This leads to uneven aeration in the tank, thereby affecting treatment performance.
2.4 Poor Management Resulting in Loss of Treatment Capacity
Due to poor management, site surveys found that the activated sludge concentration in the biological reaction tanks of the resort's wastewater treatment station is severely insufficient, and it has essentially lost its wastewater treatment capacity.
3. Technical Plan for Restoring Operation of the Wastewater Treatment Station
3.1 Design Principles of the Technical Plan
The plan should not involve adding new tank capacity, making full use of the treatment station's existing facilities and equipment, and aiming to minimize the construction period and investment costs. Implement management of laundry detergent usage and segregated pretreatment of wastewater streams. Comprehensively reduce pretreatment chemical dosing costs while ensuring the safe and stable operation of the treatment station. Adopt comprehensive technical measures to significantly enhance the treatment station's efficiency, striving for effluent compliance.
3.2 Technical Measures for Restoring Operation of the Treatment Station
Eight comprehensive technical measures are proposed to restore the treatment capacity of the resort's wastewater treatment station and achieve compliant effluent discharge.
3.2.1 Comprehensive Tank Desludging
First, remove sediment and impurities from the tank bottom. Then, fully restore the reaction tank volume. Ultimately, ensure the proper operation of aeration equipment at the tank bottom.
3.2.2 Converting the Current "Anoxic Tank" to an "Aerobic Tank"
Based on water quality test results, the NH₃-N concentration in the combined wastewater entering the station is only 13 mg/L, and DB 44/26-2001 does not impose TN removal requirements. Therefore, air pipes can be installed at the bottom of the current "anoxic tank" and fine-bubble diffusers can be arranged, converting it into an "aerobic tank." This will significantly increase the HRT of the aerobic stage, effectively enhancing the station's removal capacity for organics, NH₃-N, anionic surfactants, etc.
3.2.3 Replacing Fine-Bubble Diffusers at the Bottom of the Current "Aerobic Tank"
Replace the fine-bubble diffusers and associated air pipes at the bottom of the current "aerobic tank." Arrange fine-bubble diffusers more densely (service area < 1 m² per diffuser) to restore the fine-bubble aeration state of the "aerobic tank," strengthening the removal capacity for organics, NH₃-N, anionic surfactants, etc.
3.2.4 Enhancing Aeration Effect in Aerobic Tanks
Assess the operating status and air output of the current blower(s). If the air-to-water ratio is < 5:1, consider adding one blower dedicated to aeration for the newly converted "aerobic tank," further strengthening the removal capacity for organics, NH₃-N, anionic surfactants, etc.
3.2.5 Strengthening Sludge Recycle
Assess the operating status and flow rate of the current sludge recycle pump(s). If the flow is insufficient, replace the sludge recycle pump(s) to ensure effective return of settled sludge, improve solids separation efficiency, and prevent loss of activated sludge from the system.
3.2.6 Adding Corresponding Pretreatment Measures
Add dosing tanks (with mixers) and dosing pumps for reducing agents (ferrous chloride), pH adjustment agents (calcium hydroxide), and flocculants (polyaluminum ferric chloride). This will pretreat specific influent streams, reducing their impact on the biological system and ensuring the safe and stable operation of the treatment station.
3.2.7 Improving Operational Management Measures for the Treatment Station
Purchase essential monitoring instruments for operation management, such as sludge concentration meters, pH meters, and dissolved oxygen (DO) meters. Develop operation and maintenance manuals for the treatment station and provide targeted training for operational personnel to achieve scientific management and effective operation.
3.2.8 Enhancing Biological Treatment Capacity
Contact local wastewater treatment plants to purchase seed sludge, or purchase commercial bacterial cultures, to increase the sludge concentration in the station's biological reactors and restore/improve its biological treatment capacity.
4. Operational Effectiveness After Implementing the Renovation Plan
After conducting detailed testing and analysis of the water quality changes following the renovation of the resort's wastewater treatment station, a series of key data were obtained, as shown in Table 3. These data clearly demonstrate the significant achievements of the renovated station in removing organics, NH₃-N, and residual chlorine.
4.1 COD Removal
Regarding COD removal, a removal rate of 72.46% indicates significant progress in the degradation of organic matter by the treatment station. This is attributed to the optimization of the wastewater treatment process during the renovation, allowing organic pollutants to be decomposed and removed more effectively, thereby significantly reducing the COD content in the effluent.
4.2 BOD₅ Removal
The BOD₅ removal rate is as high as 92.10%, further demonstrating the excellent performance of the renovated station in organic matter removal. A high BOD₅ removal rate means the content of biodegradable organic matter in the effluent is greatly reduced, which is significant for protecting the water environment and preventing eutrophication.
4.3 NH₃-N Removal
Regarding NH₃-N removal, a removal rate of 60.87% also shows the high efficiency of the renovated station. NH₃-N is an important indicator of water eutrophication. A high removal rate indicates effective control of NH₃-N content in the effluent, helping to reduce the risk of eutrophication.
4.4 Total Residual Chlorine Removal
Chlorine is a commonly used disinfectant in wastewater treatment processes, but excessive residual chlorine may pose potential risks to the water environment. The removal rate for total residual chlorine by the renovated station's treatment process is 81.74%, indicating that through the station's efficient treatment, the residual chlorine content in the effluent is effectively controlled, ensuring the safety of the effluent quality.
5. Conclusion
A comprehensive analysis before the renovation of the resort's wastewater treatment station revealed that, despite reasonable process design, it had essentially lost its treatment capacity due to factors such as insufficient tank capacity, fluctuations in water quality and quantity, aging equipment and uneven aeration, and poor management. To ensure the effluent meets the primary standard (second period) values of DB 44/26-2001, the resort's wastewater treatment station underwent an upgrade and renovation. This involved strengthening water quality and quantity regulation, updating aging equipment, optimizing operational management, and employing comprehensive strategies to restore the stable operation of the treatment station. This provides solid environmental support for the sustainable development of resorts in China.