Anaerobic treatment of domestic sewage at low temperature

The main objective of this thesis was to asses the anaerobic treatment of domestic sewage at low temperature and the possibilities to optimize the performance of high-rate anaerobic systems treating domestic sewage at low temperature.The anaerobic biodegradability of domestic sewage and its fractions was investigated in batch experiments. The results showed a high potential of anaerobic treatment of domestic sewage due to its high biodegradability (74 %). The results showed a high biodegradability of the colloidal fraction (86 ± 3%) indicating that the low removal of colloidal particles in continuous high-rate anaerobic reactors is due to low physical removal rather than biodegradability.Both results of batch and continuous experiments demonstrated that the removal of SS prior to anaerobic treatment of domestic sewage not only prevents the deterioration of the methanogenic activity in the anaerobic reactor but also improves the removal of colloidal particles. Therefore, for the pre-treatment (removal of SS) of domestic sewage at a low temperature of 13 °C, a comparison between an anaerobic filter (AF) and an anaerobic hybrid (AH) reactor with flocculant sludge with an HRT of 4 h was carried out. The media in the AF and the top of the AH reactor were vertical sheets of reticulated polyurethane foam (RPF) with knobs. The sludge in the AF reactor was only attached to the media and all accumulated sludge in the bottom of the AF reactor was wasted regularly to avoid reactor clogging. The AF reactor showed a significantly higher suspended COD (COD ss ) removal (82%) than the AH reactor (53%) and the performance of the AF reactor was more stable especially in rainy periods. The results showed that the wasted sludge from the AH reactor was more stabilized. However, the wasted sludge from the AH still needs post stabilization. Therefore, the AF reactor is recommended for the pre-treatment of domestic sewage at low temperature. The results of batch experiments with RPF media with and without an anaerobic biofilm showed that the removal of COD ss in the AF reactor is mainly due to physical filtration and entrapment, while the removal of colloidal COD (COD col ) depends on the presence of a biofilm.The results of the treatment of pre-settled sewage at 13 °C demonstrated that the AH reactor with granular sludge has a significantly higher total COD (COD t ) removal than the UASB reactor due to the significantly higher COD col removal. Therefore, the AH reactor with granular sludge was selected as a second step for treatment of domestic sewage at low temperature. The performance of the AF+AH system treating domestic sewage at a low temperature of 13 °C at different HRTs was investigated. The results showed that optimization of COD ss and dissolved COD (COD dis ) in the AF and AH reactor respectively could be achieved with an HRT of 4+4 h for the two-step system without deterioration of the maximum methanogenic activity of the granular sludge in the AH reactor. For optimization of COD col a long HRT of 8 h is needed in the AH reactor. With an HRT of 4+8 h for the two-step AF+AH system, a COD t removal efficiency of 71% was achieved with 92, 60 and 55% removal efficiency for respectively COD ss , COD col and COD dis .</p

Sentiment analysis of COP9-related tweets: a comparative study of pre-trained models and traditional techniques

IntroductionSentiment analysis has become a crucial area of research in natural language processing in recent years. The study aims to compare the performance of various sentiment analysis techniques, including lexicon-based, machine learning, Bi-LSTM, BERT, and GPT-3 approaches, using two commonly used datasets, IMDB reviews and Sentiment140. The objective is to identify the best-performing technique for an exemplar dataset, tweets associated with the WHO Framework Convention on Tobacco Control Ninth Conference of the Parties in 2021 (COP9).MethodsA two-stage evaluation was conducted. In the first stage, various techniques were compared on standard sentiment analysis datasets using standard evaluation metrics such as accuracy, F1-score, and precision. In the second stage, the best-performing techniques from the first stage were applied to partially annotated COP9 conference-related tweets.ResultsIn the first stage, BERT achieved the highest F1-scores (0.9380 for IMDB and 0.8114 for Sentiment 140), followed by GPT-3 (0.9119 and 0.7913) and Bi-LSTM (0.8971 and 0.7778). In the second stage, GPT-3 performed the best for sentiment analysis on partially annotated COP9 conference-related tweets, with an F1-score of 0.8812.DiscussionThe study demonstrates the effectiveness of pre-trained models like BERT and GPT-3 for sentiment analysis tasks, outperforming traditional techniques on standard datasets. Moreover, the better performance of GPT-3 on the partially annotated COP9 tweets highlights its ability to generalize well to domain-specific data with limited annotations. This provides researchers and practitioners with a viable option of using pre-trained models for sentiment analysis in scenarios with limited or no annotated data across different domains

Modelling anaerobic digestion of concentrated black water and faecal matter in accumulation system

A dynamic mathematical model based on anaerobic digestion model no. 1 (ADM1) was developed for accumulation (AC) system treating concentrated black water and faecal matter at different temperatures. The AC system was investigated for the treatment of waste(water) produced from the following systems: vacuum toilet for black water (VBW), vacuum toilet for faeces with urine separation (VF), dry toilet (DT), dry toilets for faeces with urine separation (DF), separated faecal matter from conventional black water by filter bag (FB). For evaluation of the AC system treating the proposed waste(water) sources at 20 and 35°C, two options were studied: (1) The filling period of the AC system was constant for all waste(water) sources (either 1, 3 or 6 months) and for each period, the seed sludge volume was varied; (2) The volume of the AC system was constant for all proposed waste(water) sources. The results showed that the filling period of the AC system was the main parameter affecting the system performance, followed by operational temperature, while the increase of the seed sludge volume slightly enhanced the performance of the system. The model results indicated that the filling period of the AC system should be higher than 150 days for obtaining a stable performance. It was found that the hydrolysis of biodegradable particulate chemical oxygen demand (COD) is the rate limiting step, as volatile fatty acid concentration is very low in all experimental conditions

Enhanced primary treatment of concentrated black water and kitchen residues within DESAR concept using two types of anaerobic digesters

Anaerobic digestion of concentrated domestic wastewater streams - black or brown water, and solid fraction of kitchen waste is considered as a core technology in a source separation based sanitation concept (DESAR - decentralised sanitation and reuse). A simple anaerobic digester can be implemented for an enhanced primary treatment or, in some situations, as a main treatment. Two reactor configurations were extensively studied; accumulation system (AC) and UASB septic tank at 15, 20 and 25°C. Due to long retention times in an AC reactor, far stabilisation of treated medium can be accomplished with methanisation up to 60%. The AC systems are the most suitable to apply when the volume of waste to be treated is minimal and when a direct reuse of a treated medium in agriculture is possible. Digested effluent contains both liquid and solids. In a UASB septic tank, efficient separation of solids and liquid is accomplished. The total COD removal was above 80% at 25°C. The effluent contains COD and nutrients, mainly in a soluble form. The frequency of excess sludge removal is low and sludge is well stabilised due to a long accumulation tim