Suitability of SBR for Wastewater Treatment and Reuse: Pilot-Scale Reactor Operated in Different Anoxic Conditions

Regression-based analytical models for dissolved oxygen in wastewater

The limited freshwater resources and increasing demand for clean water require minimizing organic contamination in wastewater. High levels of biochemical oxygen demand (BOD) in water reduce available oxygen, harm ecosystem biodiversity, and degrade water quality. Here, regression-based analytical models are suggested to minimize organic contamination by estimating desired dissolved oxygen (DO) and dilution factors (df) correlated to the organic decomposition. Training datasets of defined independent inputs (i) ultimate biochemical oxygen demand (UBOD), (ii) minimum BODT (BODM), (iii) average BODT (BODA), (iv) COD, (v) O2 consumption (X), and (vi) time (T) were collected and/or calculated based on literature. Results showed that there should be specified oxygen dosing amounts dependent upon BOD5 levels, noting that BOD5 and DO5 are inversely proportional (proportionality might differ based on the microbial concentration). An increase in df is predominated by BOD5, with df≈9.2 for storm (STM), df≈12 × 103 for industrial (IND), and df≈18.5-28.5 for domestic (DOM) wastewaters. Mixing/matching between the input features used in training regressors including medium trees (MT) and ensembles boosted trees (EBT) showed high accuracy > 94% for predictor combinations: (i) MT-[UBOD-X], MT-[UBOD-X-T-COD], and EBT-[UBOD-X-T-COD] for DO5 predictions, and (ii) EBT-[BODM-BODA] and EBT-[BODM-BODA-UBOD-X-T-COD] for df predictions, knowing the general term XX-[a-b-c-d-e-f] has XX = regressor and a,b,c,d,e,f = predictors for the training parameters used as inputs. The models are capable of predicting changes in DO5 against BOD with deviations 5-10%, whereas a suggested correction factor [Formula: see text] further reduced this deviation to < 5%, where i = 0, 1, 2…6 refers to the BODM datapoint and its corresponding UBOD with the constant α = f(i). The optimized collective models (cubic equations derived for df and DO5 from BODM that is an exponent function in UBOD) would enable effluent quality evaluation to manage organic contamination, bridging the gap between science and industry best practices.

Are integrated bioelectrochemical technologies feasible for wastewater management?

The need for sustainable technological solutions for wastewater management at different scales has led to the emergence of several promising integrated bioelectrochemical technologies in the past decade. A thorough assessment of these technologies is imperative to understand their practical implementation feasibility and to identify the key challenges to prioritise the research and development work. Our multicriteria-based assessment reveals that the integrated technologies are efficient for wastewater treatment in terms of normalised land footprint [(0.31-1.39 m²/population equivalent (PE))] - and energy consumption (0.18-1.49 kWH/m³) as compared to the conventional biotechnologies, and suggests that they have potential for real-world application. Specifying the boundaries according to their treatment capabilities and scale-up potential besides niche application sites or geographical locations is required to expedite their transition to the real-world wastewater management sector.

Predicting Optimum Dilution Factors for BOD Sampling and Desired Dissolved Oxygen for Controlling Organic Contamination in Various Wastewaters

High biochemical oxygen demand (BOD) concentrations in water minimize oxygen availability, damage ecosystem biodiversity, impair water quality, and spoil freshwater. The increased level of BOD is an indication of severe organic pollution of freshwater. Thus, this study aims to establish empirical correlations between the 5-day biochemical oxygen demand (BOD5) and organic decomposition time to control organic pollution in various wastewater effluents. Ultimate biochemical oxygen demand (UBOD) and minimum and average BODt data sets along with their reaction rates were collected from earlier sampling analyses in the plants used for industrial, domestic (sanitary), and storm (surface) wastewater treatment. Average BOD5/COD ratios were then utilized to calculate existing 5-day dissolved oxygen (DO5) concentration for the estimation of experimental dilution factors (dfs) as a good start in sampling analysis to reach an optimum DO5 concentration. Moreover, the relationships between average BOD5 vs. COD, and BOD5 vs. DO5, were obtained based on the literature with 60–70% oxygen consumption rates required for organic decomposition. Results showed that such BOD5 relationships with time (power equations) or with COD (linear correlations) are helpful for wastewater engineers to generate valuable and accurate results for quality control, without the need to conduct laboratory experiments. The proposed regression equations would facilitate effluent quality assessment, allowing selection of optimal processes to control microbiological contamination or organic constituents in wastewaters.

Discovering future research trends of aerobic granular sludge using bibliometric approach

The advantageous characteristics of aerobic granular sludge (AGS) have led to their increasing popularities among academics and industrial players. However, there has been no bibliometric report on current and future research trends of AGS. This study utilized the available reports of AGS in the Scopus database for comprehensive bibliometric analyses using VOSviewer software. A total of 1203 research articles from 1997 to 2020 were analyzed. The dominance of the Netherlands and China were revealed by the high number of publications and citations. Nevertheless, the Netherlands exhibited higher average citation per article at 76.4. A recent process of AGS involving biochar and algal addition were also identified. Meanwhile, the application of AGS for antibiotic containing wastewater as well as possibility of resource recovery were recently reported and was expected to expand in the future. It was suggested that application of AGS would develop further along with the development of sustainable wastewater treatment process.

Domestic wastewater treatment in a coupled sequential batch reactor-electrochemical reactor process

The effectiveness of a sequenced biological-physicochemical reactor system for treating sewage was studied. The biological degradation was conducted in a Sequential Batch Reactor, which had innovative features for simplifying the operation and maintenance of the reactor. The reactor was operated at 4, 6, 8, and 12 hr cycle. Up to 82% removal of Chemical Oxygen Demand (COD), 50% removal of Dissolved Organic Carbon (DOC), 45% removal of Total Nitrogen (TN), and 45% removal of Total Phosphorus (TP) were achieved. The treated effluent was further polished in a continuous-flow bipolar-mode electrochemical reactor to remove additional recalcitrant organic matter from the wastewater. The process parameters were optimized using Response Surface Methodology. At the optimum condition (pH = 8.7; Current = 1.0; reaction time = 9.0), up to 90% removal of COD, 67% removal of DOC, 61% removal of TN, and 99.9% removal of TP were achieved in the coupled system. Micropollutants belonging to Pharmaceutically Active Compounds, pesticides, etc., were significantly removed. The coupled system completely removed Salmonella, Pseudomonas, and Staphylococcus. However, coliforms were detected at the outlet samples. A UV or ozone disinfection treatment is recommended for the safe reuse of the treated water for nonpotable purposes. PRACTIONER POINTS: Sequential sequential batch reactor-electrochemical reactor process (SBR-ECR) technology is effective for micropollutant removal from sewage. The coupled SBR-ECR system requires less footprint compared to conventional biological systems for wastewater treatment. Carbon material balance study revealed that more than 60% of carbon escapes from wastewater in the form of CO₂.

Statistical methods for assessing water quality after treatment on a sequencing batch reactor

Given that water scarcity is a big issue nowadays, wastewater treatment is necessary for the future water use and the prevention of environmental contamination. In this context, this study presents the results of the statistical analysis of ten water parameters before and after the water cleaning in a wastewater treatment plant (WWTP). The influent biodegradability is assessed by computing the BOD₅/COD ratio. New momentary and global efficiency indices are introduced for the evaluation of the pollutants' removal efficiency. Five classes of efficiencies (excellent, good, fair, marginal, and poor) are also proposed for the evaluation of WWTP's performances. The study shows that the WWTP's efficiency is good - when working with six water parameters - and marginal - when working with ten parameters. Small efficiencies of nitrates, total dissolved solids, and chlorine removal are noticed. Statistical distributions of ten water parameters in the influent and effluent are fitted and tested by the Kolmogorov-Smirnov and Chi-squared tests. They are utilized for computing the probability of exceeding the admissible limits of water parameters in the effluent, which can be used as a warning tool for improving the WWTP's performance.

Pilot study on urban sewage treatment with micro pressure swirl reactor

This study aimed to propose a new type of micro-pressure swirl reactor (MPSR) to treat urban sewage. The MPSR could form a stable swirl in the reactor, and realized the coexistence of anaerobic, anoxic, and aerobic zones in a single aeration tank. The pilot study showed that MPSR achieved high removal efficient of SS, COD, NH₄⁺-N, TN, TP under the conditions of drastic fluctuation in influent quality and temperature, and the average removal rate were 88.58%, 93.32%, 94.47%, 73.19%, 96.16%. The relative high abundance of Thermomonas, Thaurea, and Dechloromonas, etc, guaranteed the denitrification efficiency of the MPSR, and Dechloromonas was the main phosphorus removal bacteria in the system. The study confirmed the rationality of the structural design of the MPSR, and it was excellent in sewage treatment and stability.

Systematic Modeling of Municipal Wastewater Activated Sludge Process and Treatment Plant Capacity Analysis Using GPS-X

Mathematical modeling has become an indispensable tool for sustainable wastewater management, especially for the simulation of complex biochemical processes involved in the activated sludge process (ASP), which requires a substantial amount of data related to wastewater and sludge characteristics as well as process kinetics and stoichiometry. In this study, a systematic approach for calibration of the activated sludge model one (ASM1) model for a real municipal wastewater ASP was undertaken in GPS-X. The developed model was successfully validated while meeting the assumption of the model’s constant stoichiometry and kinetic coefficients for any plant influent compositions. The influences of vital ASP parameters on the treatment plant performance and capacity analysis for meeting local discharge limits were also investigated. Lower influent chemical oxygen demand in mgO2/L (COD) could inhibit effective nitrification and denitrification, while beyond 250 mgO2/L, there is a tendency for effluent quality to breach the regulatory limit. The plant performance can be satisfactory for handling even higher influent volumes up to 60,000 m3/d and organic loading when Total Suspended Solids/Volatile Suspended Solids (VSS/TSS) and particulate COD (XCOD)/VSS are maintained above 0.7 and 1, respectively. The wasted activated sludge (WAS) has more impact on the effluent quality compared to recycle activated sludge (RAS) with significant performance improvement when the WAS was increased from 3000 to 9000 m3/d. Hydraulic retention time (HRT) > 6 h and solids retention time (SRT) < 7 days resulted in better plant performance with the SRT having greater impact compared with HRT. The plant performance could be sustained for a quite appreciable range of COD/5-day Biochemical Oxygen Demand (BOD5 in mgO2/L) ratio, Mixed Liquor Suspended Solid (MLSS) of up to 6000 mg/L, and when BOD5/total nitrogen (TN) and COD/TN are comparatively at higher values. This work demonstrated a systematic approach for estimation of the wastewater treatment plant (WWTP) ASP parameters and the high modeling capabilities of ASM1 in GPS-X when respirometry tests data are lacking.

Real-Time Behavior of a Microalgae–Bacteria Consortium Treating Wastewater in a Sequencing Batch Reactor in Response to Feeding Time and Agitation Mode

A study of a microalgae–bacteria treatment system was conducted in a sequencing batch reactor (SBR) by combining a precultured native algae Nannochloropsis gaditana L2 with spontaneous municipal wastewater microorganisms. Two types of agitation, air mixing (AI) and mechanical mixing (MIX), were assessed at continuous illumination (L) and photoperiod cycle light/dark (L/D). The obtained consortium, via native microalgae addition, has a better operational efficiency compared to spontaneous control. This allows the removal of 78% and 53% of total Kjeldhal nitrogen (TKN) and chemical oxygen demand (COD), respectively. Under the (L/D) photoperiod, the optimal removal rate (90% of TKN and 75% of COD) was obtained by the consortium at 4 days of hydraulic retention time (HRT) using the AI mode. Moreover, during feeding during dark (D/L) photoperiod, the highest removal rate (83% TKN and 82% COD) was recorded at 4 days HRT using the AI mode. These results bring, at the scale of a bioreactor, new data regarding the mode of aeration and the feeding time. They prove the concept of such a technology, increasing the attraction of microalgae-based wastewater treatment.