Operation and recovery of a seasonally-loaded UK waste stabilisation pond system

An intermittent discharge waste stabilisation pond system was trialled for treatment of a seasonal wastewater load from a campsite. The system showed rapid acclimatisation to incoming load, with chlorophyll-a exceeding 700 mg l?1 within 2 weeks and filtered and unfiltered effluent biochemical oxygen demand below 20 and 30 mg l?1 respectively. Good performance continued for some weeks, after which photosynthetic oxygenation capacity in the first pond was seriously impaired by a shock loading believed to include fatty material. Inflow to the system was suspended and a surface film was broken up, after which the pond recovered within an 8-day period. Laboratory experiments indicated that interventions such as artificial aeration and dilution with effluent had no beneficial effect although mixing may have increased the rate of recovery

Seasonally loaded waste stabilisation ponds: a novel application for intermittent discharge

This research examined the use of a single facultative pond for treatment of an intermittent discharge from a UK campsite. The system was monitored over an 11-month period to determine the optimum time for discharge in terms of quality standards. The results showed that based on organic strength, discharge was possible in winter between November and March but February was the optimum to meet nutrient and suspended solids requirements. The pond showed rapid acclimatisation to the influent wastewater, with biochemical oxygen demand removal rates during the filling period of around 60 kg ha?1 day?1 and removal efficiencies of ?95% after maturation. The system proved simple to operate. A major design factor is the requirement for storage of net incoming precipitation, which may provide dilution of residual pollutants but requires additional system capacity.<br/

Ammonia removal in anaerobic digestion by biogas stripping: an evaluation of process alternatives using a first order rate model based on experimental findings

The feasibility of biogas stripping to remove ammonia in the anaerobic digestion of source segregated food waste was investigated. It was found in batch experiments that ammonia could be removed from digestate and that the removal followed 1st order kinetics with respect to total ammonia nitrogen concentration. Increasing temperature, biogas flow rate and initial pH all increased removal rates. Using kinetic data gathered in these experiments allowed the integration of ammonia stripping with an anaerobic digestion plant to be modelled for different configurations. Four scenarios were identified: post digestion, in situ, side-stream and pre-digestion ammonia removal relating to where in the process the ammonia stripping was performed. The modelling showed that in situ ammonia removal may be best able to reduce in-digester ammonia concentrations over a wide range of organic loading rates whereas pre-digestion showed most promise in terms of application due to the flexibility to control each part of the process separately. Further experimental work is required into these scenarios to confirm their viability

Mass transfer and gas-liquid interface properties of single CO2 bubbles rising in tap water

To improve the mass transfer efficiency in many industrial applications better understanding of the mass transfer rate is required. High speed images of single CO2 bubbles rising in tap water were analysed to investigate the relationship between the mass transfer and properties of single bubbles. Transition to a lower mass transfer rate was shown to correspond with the transition from a mobile to an immobile bubble surface. This was indicated by the change in bubble rise velocity, bubble rise path and bubble shape. The presence of surfactants in untreated tap water appear to effect the transition point, particularly for bubbles with a smaller initial diameter and lower rise velocity

Cultivation and anaerobic digestion of Scenedesmus spp. grown in a pilot-scale open raceway

Digestibility of a micro-algal mixture was evaluated by mesophilic anaerobic digestion in continuously-stirred tank reactors. The culture consisted primarily of Scenedesmus spp. continuously cultivated over a 6-month period in a 100 m2 raceway reactor instrumented to record pH, dissolved oxygen and temperature. The raceway received supplementary carbon in the form of flue gas from a diesel boiler (10% CO2) injected into a 1-m deep sump to control pH in the range 7.8–8.0. Dilution was optimised to biomass productivity and gave values of 10–15 and 20–25 g total suspended solids (TSS) m? 2 day? 1 in winter (December–February) and spring (April–May), respectively. The culture for the anaerobic digestion trial was harvested in February by centrifugation to give an algal paste containing 4.3% volatile solids (VS). Semi-continuous digestion at organic loading rates of 2.00, 2.75 and 3.50 g VS l? 1 day? 1 gave volumetric biogas productions of ~ 0.66, ~ 0.83 and ~ 0.99 l l? 1 day? 1, respectively. Specific methane yield ranged from 0.13 to 0.14 l CH4 g? 1 VSadded with biogas methane content ~ 62%. Overall the digestion process was stable, but only ~ 30% VS destruction was achieved indicating low biodegradability, due to the short retention times and the recalcitrant nature of this type of biomas

Effect of a trace element addition strategy on volatile fatty acid accumulation in thermophilic anaerobic digestion of food waste

PurposeA trace element (TE) supplementation strategy previously shown to be effective in mesophilic conditions was tested for thermophilic digestion of source segregated domestic food waste.MethodsInoculum from a mesophilic anaerobic digester treating municipal wastewater biosolids was successfully acclimated to thermophilic temperature (55 °C) with food waste as a substrate. Four laboratory-scale digesters were maintained at a loading of 2 g VS l?1 day?1 with one pair receiving TE supplementation. Two more pairs of digesters were incrementally loaded to 3 and 4 g VS l?1 day?1, respectively, and also received TE.ResultsAll digesters performed well for the first 3–4 months of operation, but volatile fatty acid (VFA) concentrations in those without TE showed no recovery from an initial small accumulation. On continued operation, VFA concentrations increased in all digesters, especially those at higher loading rates or without TE supplementation, reaching &gt;30 g l?1. Under these meta-stable conditions, a deliberate disturbance to daily feeding (cessation then resumption) led to acetic acid accumulation, a fall in pH and a sharp increase in the ratio of partial to intermediate alkalinity. Increases in VFA corresponded to an increasing total ammonia nitrogen concentration which appeared to become inhibitory at ~2,500 mg N l?1.ConclusionsWhile TE supplementation delayed the onset and reduced the rate of VFA accumulation, it was unable to sustain stable digestion of this substrate in thermophilic conditions.<br/

Energy balance of algal biogas production

A mechanistic energy balance model was successfully developed for the production of biogas from the anaerobic digestion of micro-algal biomass from raceways. The energy balance model was used to consider the energetic viability of a number of production scenarios, and to identify the most critical parameters affecting net energy production. The output of the model demonstrated that no single method of harvesting studied (centrifugation, settlement or flocculation), produced a sufficiently greater energy output over operational energy inputs to make algal biogas production viable. Combinations of harvesting methods produced energy outputs 2.3 to 3.4 times greater than the operational energy inputs. Electrical energy to power pumps, mixers and harvesting systems is 5 to 8 times greater than the heating energy requirement. If the energy to power the plant is generated locally in a combined heat and power unit a considerable amount of “low grade heat” will be generated that is not required by the algal biogas process and for the plant to be efficient must be exploited. It is concluded that the production of micro-algal biogas may be energetically viable, but is dependent on the exploitation of the heat generated by the combustion of biogas in combined heat and power units to show a positive balance

Special and Inclusive Teachers’ Experience in The Distance Learning

This study was designed to explore the lived experiences of special and inclusive teachers in distance learning and gained necessary perspective about their different experiences and challenges in the new normal education in distance learning. It utilized the use of phenomenological research design and simple random sampling on choosing the participants. Data were analyzed through thematic analysis method. The results indicated that the teachers felt inadequately prepared to teach atypical learners in distance learning because of some factors, examples are lack of resources of teachers and students. Almost all participants indicated that they discovered their own teaching strategies in handling atypical learners. In addition, the teachers make use of the available technology by utilizing different educational applications. Also, the majority of the teachers motivate their students to continue to learn in the new normal. Implications of these results are discussed

Operation and recovery of a seasonally-loaded UK waste stabilisation pond system

An intermittent discharge waste stabilisation pond system was trialled for treatment of a seasonal wastewater load from a campsite. The system showed rapid acclimatisation to incoming load, with chlorophyll-a exceeding 700 mg l?1 within 2 weeks and filtered and unfiltered effluent biochemical oxygen demand below 20 and 30 mg l?1 respectively. Good performance continued for some weeks, after which photosynthetic oxygenation capacity in the first pond was seriously impaired by a shock loading believed to include fatty material. Inflow to the system was suspended and a surface film was broken up, after which the pond recovered within an 8-day period. Laboratory experiments indicated that interventions such as artificial aeration and dilution with effluent had no beneficial effect although mixing may have increased the rate of recovery

HbA1cmeasurement and relationship to incident stroke

Aims: To determine the proportion of people with diabetes who have Hb A1c measured, what proportion achieve an HbA1c level of &lt; 58 mmol/mol (7.5%), the frequency of testing and if there was any change in HbA1c level in the year before and the year after an incident stroke. Methods: This study used the Secure Anonymised Information Linkage (SAIL) databank, which stores hospital data for the whole of Wales and ~65% of Welsh general practice records, to identify cases of stroke in patients with diabetes between 2000 and 2010. These were matched against patients with diabetes but without stroke disease. We assessed the frequency of HbA1c testing and change in HbA1c in the first year after stroke. Estimation was made of the proportion of patients achieving an HbA1c measurement ≤ 58 mmol/mol (7.5%). Results: There were 1741 patients with diabetes and stroke. Of these, 1173 (67.4%) had their HbA1c checked before their stroke and 1137 (65.3%) after their stroke. In the control group of 16 838 patients with diabetes but no stroke, 8413 (49.9%) and 9288 (55.1%) had their HbA1c checked before and after the case-matched stroke date, respectively. In patients with diabetes and stroke, HbA1c fell from 7.7 to 7.3% after their stroke ( P&lt;0.001). Before the study, 55.0% of patients with stroke had an HbA1c ≥58 mmol/mol compared with 65.2% of control patients, these figures were 62.5% and 65.3% after the stroke. Conclusions: The frequency of diabetes testing was higher in patients who had experienced a stroke before and after their incident stroke compared with control patients but did not increase after their stroke. Glucose control improved significantly in the year after a stroke