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

Anaerobic digestion of domestic sewage al low temperature

The results of research concerning the feasibility of anaerobic treatment of domestic sewage at low temperature are summarized in this article. The batch tests demonstrated a high biodegradability of domestic sewage at 20°C (74Ž Both batch and continuous experiments for the treatment of domestic sewage showed that the removal of SS prior to anaerobic treatment of domestic sewage not only provides a stable reactor performance but also improves the removal of both colloidal (CODcol) and dissolved COD (CODdis). The results of the pre-treatment of domestic sewage in an anaerobic filter (AF) and an anaerobic hybrid (AH) reactor showed that the AF reactor is an efficient process for the removal of suspended COD (CODss), viz. 82°at an HRT of 4 h and 13°C. The novel AF reactor consists of vertical sheets of reticulated polyurethane foam with knobs, where the biomass was only in attached form. For the treatment of pre-settled sewage at 13°C, the AH reactor, with granular sludge, showed a higher total COD (CODt) removal than the UASB reactor as a result of higher CODcol removal. Therefore, the performance of a two-step system, AF AH (with granular sludge) reactor, was investigated with different HRTs at 13°C. For optimization of CODss and CODdis an HRT of 4 4 h is needed, while for optimization of CODcol removal an HRT of 4 8 h is required. A CODt removal of 71 as achieved with 60␌onversion to methane from the removed CODt when the AF AH system was operated at an HRT of 4 8 h at 13°C

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

Treatment of domestic sewage in a two-step system anaerobic filter/anaerobic hybrid reactor at low temperature

The treatment of domestic sewage at low temperature of 13 degrees Celsius was investigated in a two-step system consisting of an anaerobic filter (AF) + an anaerobic hybrid (AH) reactor operated at different hydraulic retention times (HRTs

Low temperature pre-treatment of domestic sewage in anaerobic hybrid and anaerobic filter reactor

The pre-treatment of domestic sewage for removal of suspended solids (SS) at a process temperature of 13 degreesC and an hydraulic retention time (HRT) of 4 h was investigated in an anaerobic filter (AF) and anaerobic hybrid (AH) reacto