A simple respirogram-based approach for the management of effluent from an activated sludge system

Evaluating river health through respirogram metrics: Insights from the Weihe River basin, China

Human activities pose a significant threat to rivers, requiring robust assessment methods for effective river management. This study focuses on the Weihe River Basin in Shaanxi province and introduces the respirogram as an innovative assessment technique. The respirogram allows the simultaneous assessment of river health from two important aspects: pollution levels and microbial status. Specifically, the in-situ respiration ratio (Rs/t) serves as an indicator of pollution, with higher Rs/t values correlating with increased pollution levels. Conversely, the recovery index (RI) measures microbial vitality, with values below 0.15 indicating greater microbial activity and recovery potential. Using predefined thresholds of Rs/t = 0.3 and RI = 0.15, water bodies were categorized into four types. For example, rivers with Rs/t > 0.3 and RI > 0.15 were identified as receiving sewage, characterized by high pollution and low microbial vitality. Similarly, different assessment criteria delineated urban rivers, natural rivers, and wastewater treatment plants. Based on these classifications, targeted engineering measures were proposed to enhance the self-purification capabilities of rivers of different statuses.

A novel approach to estimate and control denitrification performance in activated sludge systems with respirogram technology

Respirogram technology has been widely applied for aerobic process, however, the response of respirogram to anoxic denitrification is still unclear. To reveal such response may help to design a new method for the evaluation of the performance of denitrification. The size distribution of flocs measured at different denitrification moments demonstrated a clear expansion of flocs triggered by denitrification, during which higher specific endogenous and quasi-endogenous respiration rates (SOUR_e and SOUR_q) were also observed. Furthermore, SOUR_q increases exponentially with the specific denitrification rate (SDNR), suggesting that there should be a maximum SDNR in conventional activated sludge systems. Based on these findings, an index R_q/t, defined as the ratio of quasi-endogenous (OUR_q) to maximum respiration rate (OUR_t), is proposed to estimate the denitrification capacity that higher R_q/t indicates higher denitrification potential, which can be readily obtained without complex measurement or analysis, and it offers a novel and promising respirogram-based approach for denitrification estimation and control by taking measures to extend anoxic time to maintain its value at a high level within a certain range.

Novel Quantitative Evaluation of Biotreatment Suitability of Wastewater

The development of wastewater treatment industry has gradually entered the high-standard period and the wastewater treatment technology needs to be refined for different types of wastewater. Traditional water quality indicators are not able to explain new problems encountered in the current wastewater treatment process, especially the potential of removing pollutants via biological methods. This research proposed a new method of evaluating the biological treatment process by measuring the oxygen consumption in the biodegradation of pollutants on-the-go and describing the complete biological oxygen consumption process. The biodegradability of wastewater from an actual textile wastewater treatment plant was quantitatively evaluated by analyzing the proportion of different organic pollutions. Results showed that the hydrolytic acidification can improve the biodegradability of textile wastewater by increasing the content of biodegradable organic matter (growth of 86.4%), and air flotation has little effect on the biodegradability of the wastewater. Moreover, the biodegradability of the textile wastewater could be improved by increasing the nitrogen and phosphorus content, which could come from urea and K2HPO4. Concretely, nitrogen source mainly increases organic matter of rapid bio-treated and organic matter of easy bio-treated by 14.94% and 70.79%, and phosphorus source mainly increases the organic matter of easy bio-treated by 143.75%. We found that the optimum concentration of additional N and P to the textile wastewater was 35 mg/L and 45 mg/L, respectively. This approach holds great application prospects such as risk control, optimizing treatment technology, and management, due to its characteristics of being simple, easy to use, and rapid online implement action.

A new approach to evaluate and improve the stability of aerobic sludge systems based on maintenance coefficient

Stability is a key issue of wastewater treatment plants using either aerobic granular (AGS) or conventional activated sludge (CAS). The two forms of aerobic sludge were cultivated under different conditions to study the main factors affecting their stability. It was found that maintenance coefficient (m) describing the fraction of non-growth energy of granules increased significantly when the system became more stable during processes with the enhancement of granulation and the periodic short-term shock load. The yield coefficient (Y_H) was the main factor affecting the m value, and the inhibition in Y_H value was able to promote the maintenance potential according to the kinetic equation. Therefore, strategies that promote the maintenance coefficient could be applied to improve the stability of sludge systems, including inhibiting the yield rate and taking periodic short-term shock. Evaluation of stability based on the maintenance coefficient is a promising tool for ensuring the stable operation of wastewater treatment processes.

Simultaneous evaluation of bioactivity and settleability of activated sludge using fractal dimension as an intermediate variable

Bioactivity and settleability of activated sludge are essential for the operation of activated sludge systems in wastewater treatment. In this work, the fractal dimension of sludge image is proposed as a tool to evaluate these two factors. The specific endogenous respiration rate (SOUR_e) and the specific quasi-endogenous respiration rate (SOUR_q) are found to be more dependent on the 3D structure of sludge than the specific total respiration rate (SOUR_t). The relationship between the fractal structure and bioactivity suggests that the bioactivity governs the acceptable upper bound of the fractal dimension (D_f), as at its theoretical maximum of 2.0, the non-porous compact flocs are predominant. The settleability or the biomass concentration determines the acceptable lower bound of D_f, as at its theoretical minimum of 1.0, the free-swimming microbes are predominant. Our data reveal that the activated sludge has an acceptable fractal dimension D_f in a range of 1.07-1.68. In practice, the fractal dimension should be controlled at a reasonable value as there is a trade-off between the bioactivity and physical structure to achieve better performance. A decrease or increase in the fractal dimension can serve as a signal for the change of the operational status, and this is further elucidated from the perspective of settling tanks using state point analysis. Compared with respirogram measurement, measuring fractal dimension is a complex process and its online implementation is challenging. Also, the measured value varies with the methods used. In addition, the difference in their theoretical values depends on the homogeneity of the sludge structure. Since the fractal dimension D_f reflects both bioactivity and settleability of the sludge but is difficult to measure, in this work a relationship between D_f and the easily measurable respirogram is established, and a method using the respirogram as a proxy of D_f is proposed to control the bioactivity and settleability simultaneously. This respiration-based method is able to simultaneously control aeration and settling tanks, and could serve as an efficient tool for the management of wastewater treatment plants.

Activated sludge and other aerobic suspended culture processes

The fields in the process model of activated sludge, the characteristics and species of microbial communities, dynamics and mechanism in the process, the influence of different xenobiotics on activated sludge, anaerobic digestion on waste activated sludge, and design and operation for activated sludge are reviewed in 2018. Contrast with the past reviews, several new highlights such as waste activated sludge treatment, antibiotic and heavy-metal xenobiotic, and pretreatment for anaerobic digestion are mentioned in 2018, which indicated that the research tendency of activated sludge from wastewater treatment to waste sludge treatment in the retrieved literature is developing. PRACTITIONER POINTS: None.

Tuning of activated sludge in winter based on respirogram profiles under standard and site temperatures

Respirograms of activated sludge OUR^T_x and OUR²⁰_x were measured under site (T) and standard (20°C) temperatures, respectively, and the predicted standard temperature respirogram OUR²⁰_x,cal was also calculated using the Arrhenius equation. These respirogram profiles reveal more information than effluent quality. A decrease of OUR²⁰_x is a critical alarm signal for the loss of pollutant removal capacity, and a sudden increase of the predicted value OUR²⁰_x,cal is an alarm signal for the unrecoverable deterioration of biomass. The sign of OUR²⁰_x-OUR²⁰_x,cal can be used for selection of tuning strategies. For example, a negative value of OUR²⁰_x-OUR²⁰_x,cal indicates that doubling biomass is difficult, thus strategies such as extending the reaction time with limited available biomass is preferred. The findings in this study elucidated the respiration profile of activated sludge under changes of temperature and can be effectively used for the stable operation of Wastewater Treatment Plants under cold temperatures and seasonal variations.

Probing operational conditions of mixing and oxygen deficiency using HSV color space

In this work, the relationship between sludge color and operational conditions was studied. It was found that the coordinates H and S of the HSV color space well correlated with biological status and the operational conditions of mixing and oxygen deficiency, and a coefficient of variation (CV_H/S) of the ratio of H to S in sludge cake images was derived. A smaller CV_H/S indicated better mixing conditions based on the observations of four laboratory-scale experiments and two full scale WWTPs, which can be used as a promising index for the monitoring of mixing condition. The coordinate oxygen uptake rate (OUR_q) of the respirogram space showed similar trend as CV_H/S, and analysis of microbial community also showed that CV_H/S could indicate changes of biological community including species and richness. These findings suggested that CV_H/S is a biological meaningful index for detecting the effect of changing operational conditions, which gives a key to quantify a large number of empirical rules accumulated in the past. Furthermore, it promotes the Internet of Things (IoT) application to the management of WWTPs, as color is readily available with MEMS (Micro-Electro-Mechanical Systems) sensors such as smart phones.