Palm oil refinery wastes treatment

Effluent from the refining of crude palm oil was subjected to physical-chemical and biological treatment. An inclined corrugated parallel plates oil separator spaced at 25 mm was used with hydraulic loading rates of 0.2, 0.5 and 1 m³ m⁻²-h. 91% oil and grease removal could be achieved at 0.2 m³ m⁻²-h. Coagulation and flocculation carried out on batch samples after oil and grease separation revealed that with 100 mg l⁻¹ alum addition BOD was reduced from 3500 to 450 mg l⁻¹ and COD from 8600 to 750 mg l⁻¹ after 30 min settling. Higher doses of alum and doses of polyelectrolyte, activated carbon and sodium hypochloride did not yield significant additional reductions in BOD and COD. Batch dissolved air flotation (DAF) removed 90% of the suspended solids with 2.7% solids in the thickened sludge at an A/S ratio of 0.014. This method yielded the similar effluent quality as the inclined corrugated plates oil and grease separator. Field data from a DAF plant compare closely with data achieved in this study. Activated sludge treatment on the effluent from the oil separator yielded a BOD of 46 mg l⁻¹ with a loading rate of 0.3 g BOD (g MLVSS)⁻¹-day. Total dissolved solids (TDS) remained high and removal through coagulation and chemical oxidation brought the COD level down to around 180 mg l⁻¹. Biokinetic coefficients Y, k_dK and K₃ were found to be 0.85 g VSS (g BOD)⁻¹, 0.016 day⁻¹, 0.12 g BOD (g VSS)⁻¹-day and 510 mg l⁻¹ BOD respectively.     

High-rate overland flow

Recommended loading rates for treating raw domestic wastewater by overland flow are 6.3–15 cm wk⁻¹. Information provided in the literature yields little insight regarding the upper range of hydraulic loading rates that could be effectively treated by overland flow. Therefore, field investigations were conducted to evaluate the performance of the overland flow system at overland flow rates from 0.95 m³ day⁻¹ m⁻¹ width of slope (13 cm wk⁻¹ to 4.15 m³ day⁻¹ m⁻¹ (57 cm wk⁻¹).Preliminary treated municipal wastewater was pumped to overland flow slopes, each approx. 3.7 m wide and 36.5 m long. The slope of each plot was 2.5%. The cover crop consisted of a mixture of ryegrass, bluegrass and fescue grass. The plots were operated for 2 years at six different hydraulic loading rates.Effluent BOD₅ concentration averages varied from 6 to 11 mg l⁻¹. The reduction of influent BOD₅ concentration ranged from 87 to 93%. Mean effluent suspended solids values were from 6 to 9 mg l⁻¹ with reductions of influent concentrations of 91–95%. Hydraulic application rate had little effect on percent BOD₅ or suspended solids removal.Total phosphorus reductions were minimal at all hydraulic application rates due to limited soil water contact.Ammonia concentration in the effluent ranged from 1 mg l⁻¹ NH₃-N at the 0.95 m³ day⁻¹ m⁻¹ (13 cm wk⁻¹) applied flow rate of 11.7 mg l⁻¹ NH₃-N at the 4.15 m³ day⁻¹ m⁻¹ (57 cm wk⁻¹) loading rate. Ammonia and nitrogen reductions decreased as the applied flow rate increased. Consequently, lower overland flow rates are necessary for nitrogen removal.The use of high-rate overland flow could potentially reduce the land necessary for this form of land application, if nutrient removal was not a local concern.     

An automated determination of low reactive phosphorus concentrations in natural waters in the presence of arsenic, silicon and mercuric chloride

An automated technique for reactive phosphorus, sensitive to <0.5 mg P m⁻³, is described. Interference from AsO³⁻₄-As and mercuric chloride is removed by thiosulphate in acid solution. The interference from 100 mg AsO³⁻₄-As m⁻³, 10 g m⁻³ molybdate-reactive silicon or 60 g m⁻³ mercuric chloride is equivalent to <0.5 mg P m⁻³.     

The effects of geology and land use on the export of phosphorus from watersheds

The export of total phosphorus from 34 watersheds in Southern Ontario was measured over a 20-month period. The annual average export for igneous watersheds (i.e. those of the Canadian Shield) that were forested was 4.8 mg m⁻² yr⁻¹, significantly different from the average (11.0 mg m⁻² yr⁻¹) for watersheds that included pasture as well as forest. Similarly, on sedimentary rock, the mean export from forested watersheds (10.7 mg m⁻² yr⁻¹) differed significantly from those with forest and pasture (28.8 mg m⁻² yr⁻¹). The differences between watersheds of different geology but similar land use were also highly significant.Additional data from the literature supported our conclusions. Other forested igneous watersheds of plutonic origin averaged 4.2 mg m⁻² yr⁻¹ of total phosphorus exported: forested igneous watersheds of volcanic origin, however, averaged 72 mg m⁻² yr⁻¹. The overall average export from each type of watershed as classified by geology and land use was very similar to that for the same classification found in our study.The effects of agriculture and urbanization were to greatly increase the total phosphorus exported. Wide ranges of values probably reflect the intensity of land use.     

Hypolimnetic aeration: field test of the empirical sizing method

A hypolimnetic aeration system was recently installed in a small (16 ha S_α) eutrophic lake and a comparison made between measured performance and predicted performance from an empirical sizing method. The design variables used to size the system were: hypolimnetic volume 451,600 m³; maximum hypolimnetic oxygen consumption 0.2 mg l⁻¹ d⁻¹; aerator input rate 2 mg l⁻¹; water velocity 0.76 m s⁻¹ and depth of air release 12.2 m. A 3.7 kW compressor (0.57 m³ min⁻¹) generated a water velocity of 0.46 m s⁻¹, a water flow of 17.7 m³ min⁻¹ and a theoretical hypolimnetic circulation period of 18 days. Dissolved oxygen increased by an average of 1.6 mg l⁻¹ on each cycle through the aerator, and aerator input rates ranged from 0.6 to 2.6 mg l⁻¹. Hypolimnetic oxygen consumption averaged 0.12 mg l⁻¹ d⁻¹ and ranged between 0.02 and 0.21 mg l⁻¹ d⁻¹. The aeration system was unable to meet the daily oxygen demand (90 kg) as the water velocity was slower than expected (0.46 m s⁻¹). To avoid undersizing future aeration installations the following recommendations should be considered when using the empirical sizing formula: (1) estimates of oxygen consumption should be annual maximums from aerobic hypolimnia; (2) aerator input rates should be conservative (e.g. 1–4 mg l⁻¹) and increase with depth; (3) water velocity of 0.45–0.50 m s⁻¹ should initially be used when no information on actual bubble size or velocity is available; (4) aeration start-up should be timed to avoid periods of accumulated oxygen demands.     

Treatment of poultry manure wastewater using a rotating biological contactor

A pilot scale, six stage rotating biological contactor was used to evaluate the feasibility of this process for the stabilization of liquid animal manures. Total disc surface area was approx. 16.7 m². Treatment efficiencies were determined at various waste strengths and influent flow rates.With loading rates of 14.7–322 g m⁻² day⁻¹, the average COD reduction was 61%. With loading rates of 4.88-24.4 g m⁻² day⁻¹, the average BOD₅ reduction was 87%. Total nitrogen removal averaged approximately 30% for the entire study. Mixed liquor oxygen uptake rates were generally in excess of 80 mg 1⁻¹ h⁻¹.Clarified effluent was non-odorous and suitable to be reused for manure flushing or spray irrigation. Treatment was not sufficient to permit effluent discharge to surface waters.     

An improved hydrazine reduction method for the automated determination of low nitrate levels in freshwater

An automated nitrate determination is described in which nitrate is reduced to nitrite with hydrazine sulphate under alkaline conditions in the presence of Cu²⁺ and Zn²⁺. Interferances encountered in natural water samples were eliminated by the addition of Zn²⁺ to the Cu²⁺ catalyst solution.The method is suitable for the determination of low NO₃−N concentrations and compares favourably with the manual copperised cadmium technique for freshwater samples containing 10–800 mg m⁻³ NO₃−N. The method is also linear at nitrate concentrations below 10 mg N m⁻³. The standard deviations (S.D.) of blanks and of samples containing 2 mg NO₃−N m⁻³ were 0.013 and 0.06 mg N m⁻³ respectively at an analysis rate of 30 samples h⁻¹.     

The use of an upflow fixed bed reactor for treatment of a primary settled domestic sewage

This study presents and demonstrates results obtained from an half full-scale upflow fixed bed reactor (UFBR) treating a primary settled domestic sewage. This study used expanded clay with an effective size of 2.7 mm containing hematite and magnetite as a granular medium.The content of TSS in the effluent treated was always between 10 and 20 mg l⁻¹ for bed depths ranging from 2 to 3 m and filtration rates of 3–6 m³m⁻²h⁻¹.The profiles taken all along the reactor show that the activity of the biomass is constant over the whole height of the reactor. Moreover, an air/water volume ratio of 2:1 is amply sufficient to satisfy the oxygen demand of the biomass. The average removal efficiency based on the soluble COD remains virtually unchanged as a function of the filtration rate at about 70% of the influent. For a final BOD₅ of 30 mg l⁻¹, loadings of 4.5–8 kg BOD₅m⁻³ can be applied. This corresponds to filtration rates of 3–6 m³m⁻²h⁻¹. The removal efficiencies for BOD₅ are then about 80%.After optimization of the backwashing conditions, the consumption of backwash water is about 5% of the volume of filtered water.Sludge measurements carried out during our experiments indicate an excess sludge production of 1 kg kg⁻¹ BOD₅ eliminated. The nature of these sludges is very similar to the biological sludges produced in the high rate activated sludge process.This study has made it possible to establish design parameters of an UFBR and to develop technology for applications. These results are applied to two wastewater treatment plants which began to operate in 1984: these plants serve population equivalents of 40,000 and 11,000.     

Comparative pilot-scale investigation into uprating the performance of percolating filters by partial medium replacement

A pilot-scale investigation was carried out to ascertain whether the loading to conventional single-pass percolating filters could be increased by partially replacing mineral medium with a random plastic medium. The treatment efficiency of a mixed-media filter (1.2m³ blast furnace slag topped by 0.8 m³ Flocor RC plastic medium) was compared over 26 months with the treatment efficiencies of two single-medium filters containing 2 m³ blast furnace slag and 2 m³ Flocor RC respectively. Two hydraulic loadings, 1.68 and 3.37 m³ m⁻³ d⁻¹, average organic loadings 0.28 and 0.63 kg BOD m⁻³ d⁻¹, were used for consecutive periods of 13 months. Medium replacement has been shown to be a viable system for uprating conventional filters. The mixed filter was more versatile and was also markedly more efficient than the slag filter at the higher hydraulic loading. It is estimated that at this loading the mixed filter could treat a 30% greater organic load than the slag filter.     

Anaerobic filter treatment of molasses distillery slops

Anaerobic filter treatment of beet molasses distillery slops was carried out in laboratory and pilot scale reactors. During a one year operation period volumetric loadings of up to 50 kg VS m⁻³ d⁻¹, corresponding to a hydraulic residence time of approx. 1 day, were achieved. The biogas yield was between 430 and 460 l kg VS⁻¹ resulting in a gas productivity of between 13 and 20, 5 m³ m⁻³ d⁻¹.     

Mercury fluxes in a natural forested Amazonian catchment (Serra do Navio, Amapá State, Brazil)

Mercury (Hg total) fluxes were calculated for rainwater, throughfall and stream water in a small catchment located in the northeastern region of the Brazilian Amazon (Serra do Navio, Amapá State), whose upper part is covered by a natural rainforest and lower part was altered due to deforestation and activities related to manganese mining. The catchment area is 200 km from the nearest gold mining (garimpo). Minimum and maximum Hg concentrations were measured monthly from October 1996 to September 1997 and were 3.5–23.4 ng l⁻¹ for rainwater, 16.5–82.7 ng l⁻¹ for throughfall (March–August 1997) and 1.2–6.1 and 4.2–18.8 ng l⁻¹ for stream water, in natural and disturbed areas, respectively. In the natural area, the inputs were 18.2 μg m⁻² year⁻¹ in rainwater and 72 μg m⁻² year⁻¹ in throughfall. This enrichment was attributed to dry deposition. The stream output of 2.9 μg m⁻² year⁻¹ indicates that Hg is being recycled within the forest as other chemical species or is being retained by the soil system, as confirmed by the cumulative Hg burden in the 0–10 cm surface layer, which was 36 480 μg m⁻². When the disturbed area of the catchment was included, the stream output was 9.3 μg m⁻², clearly indicating the impact of the deforestation of the lower part of the basin on the release of mercury. The Hg burden in the disturbed area was 7560 μg m⁻² for the 0–10 cm surface layer.     

Field studies on coliphages and coliforms as indicators of airborne animal viral contamination from wastewater treatment facilities

The occurrence of animal viruses in the aerosol emissions of wastewater treatment facilities was evaluated by direct assay and by the use of coliforms and coliphages as indicator organisms. Coliforms and coliphages were compared and evaluated with regard to their suitability as indicators of airborne animal viral contamination from wastewater treatment facilities. Two plants, one with treatment by activated sludge and the other by trickling filtration, were studied. Field air sampling procedures used large-volume air samplers, with recirculation devices, and Andersen samplers. Airborne viruses were enumerated by a most probable number (MPN) procedure. Partially treated liquid sewage contained about 1.0 × 10² pfu l⁻¹ of animal viruses assayed on Buffalo Green Monkey (BGM) cells, 3.6 × 10⁵ and 5.0 × 10⁵ pfu l⁻¹ of coliphages, depending upon the E. coli host strain used for assay, and 2.0 × 10⁹ colonies l⁻¹ of coliform bacteria. No airborne animal viruses were recovered, airborne coliphage levels averaged 2.3 × 10⁻¹ and 3.0 × 10⁻¹ MPN m⁻³, coliforms from aerosol emissions were 2.1 × 10² colonies m⁻³. Ratios of coliphages to animal viruses indicate that wastewater treatment plants may be continuous sources of low level concentrations of animal virus aerosols. Evidence shows coliforms to be much less stable than coliphages in the airborne state. Coliphages may be a more acceptable indicator of airborne animal viral contamination than coliforms.     

Removal of humic substances from natural waters by reverse osmosis

An investigation of the potential use of reverse osmosis for the removal of humic substances in order to remove colour and haloform precursors in small waterworks has been carried out, using three different laboratory scale reverse osmosis units and several different membranes.Membrane pore size was found to be the most important factor that influenced both the permeate quality and the product water flux. Pressure was found to have no significant influence on permeate quality, but was linearly related to product water flux. The concentration of humic substances in the influent was not found to affect product water flux but the transport of humics across the membrane was found to be dependent upon influent concentration. For the selected membranes, the removal of humic substances amounted to 80–100% in terms of colour removal, and 50–99% in terms of permanganate value reduction. The most suitable membranes for the different available units were found to be Osmonics SEPA 89 (permeate flux 251 m⁻² h⁻¹ at 15 bars), DDS 865 (permeate flux, 1201 m⁻²h⁻¹ at 40 bars) and PCI T2A (permeate flux 901 m⁻²h⁻¹ at 20 bars). At suspended solids concentrations higher than 100 mg 1⁻¹ of bentonite, product water flux was significantly reduced.     

The quality of run-off from an irrigated market garden area in Brazil

This paper presents the results of a study carried out in Brazil to determine the effects of irrigation and fertiliser use on the quality characteristics of run-off from an agricultural area used for intensive cultivation of market garden produce.The results show that during dry weather the discharge of nutrients from the cultivated area when irrigation is taking place is equivalent to 7 kg ha⁻¹ yr⁻¹ N and 1 kg ha⁻¹ yr⁻¹ P. Considerable accumulation of nutrients took place in the soil during the growing season, over the 129-day survey period the nutrient content of the top soil increased by approximately 590 g m⁻²N and P and 780 g m⁻²K. This accumulation was derived from fertilisers which were applied at rates of 1136 kg ha⁻¹N, 978 P and 1367 K. During wet weather the nutrients which had accumulated in the soil were washed out.     

Use of large submerged chambers to measure sediment-water interactions

Submerged chambers were designed and constructed primarily to study in situ sediment phosphorus release in Shagawa Lake, Minnesota. Initial experiments indicated anoxic phosphorus release rates of 7 mg m⁻² day⁻¹. Oxygen consumption rates within the chambers were also measured; an average consumption rate of 0.17 g m⁻² day⁻¹ was obtained.     

Passive reduction of human exposure to indoor ozone

Reactive building materials offer an opportunity to provide indoor air cleaning with minimal energy use. Laboratory and test house experiments provide evidence that indoor ozone concentrations can be diminished by activated carbon (AC) and unpainted gypsum wallboard (GWB) panels. These two materials are highly reactive with ozone and produce few byproducts. When measured in a 14.2 m³ stainless-steel chamber, the mean deposition velocities to the materials were 5.3 m h^-1 for AC and 2.4 m h⁻¹ for GWB for a variety of airflow and relative humidity conditions. The ozone decay rates for both the materials were also measured in an unoccupied 34.5 m³ bedroom under various mixing conditions. In this case, ozone removal increased relative to background by 27–100% with a 4.4 m² panel of a reactive material placed on one wall of the bedroom. The ozone decay rate for the bedroom increased over background by approximately 2–3 h⁻¹ for GWB and 2–7 h⁻¹ for AC. Application of a mass balance model for a typical home demonstrates that effectiveness for ozone removal depends weakly on the air exchange rate and strongly on the panel material, panel area, and mixing conditions. An ozone removal effectiveness of over 80% is possible with sufficient panel area and positioning that provides elevated air speeds near the panels.     

An interlaboratory study of dissolved oxygen in water

Dissolved oxygen concentrations in water samples free from chemical reductants may be stabilised by the addition of mercuric chloride (40 g m⁻³) and storage in gas-tight bottles. This preservation technique has been used in an interlaboratory study of dissolved oxygen analysis in New Zealand laboratories. At reference concentrations of 1.20 and 5.86 g m⁻³, there was a significant positive bias in results reported for both the Winkler method (0.24 and 0.22 g m⁻³ respectively) and the membrane electrode method (0.59 and 0.62 g m⁻³ respectively). Inadequate precautions to avoid sample aeration during handling and analysis probably caused the bias.     

Operating characteristics of the aerated submerged fixed-film (ASFF) bioreactor

A multi-stage fixed-film reactor was developed in which a stationary submerged biofilm is attached to ceramic tiles under diffused aeration. Tracer studies revealed that the reactor's hydraulic regime is described by a CSTR-in-series model. Reactor performance at 20 °C was examined using sucrose wastewaters with organic strength up to 900 mg l⁻¹ COD, at hydraulic loadings up to 0.1 m³ m⁻²d⁻¹ and organic loadings up to 90 g CODm⁻² d⁻¹. The reactor demonstrated the capability of achieving 97% soluble COD removals at low loadings and exhibited efficient and stable performance at high hydraulic and organic loadings. Even at application rates near the rate-limiting mass loadings, there was only a 9% loss in efficiency. Reactor operation at high loadings appears to be advantageous since organic substrate removal rates and attached biomass per unit surface area increased with the increase in organic loading. This can be attributed to the good oxygen transfer and the considerable quantity and type of attached biomass attained. Staging of the reactor proved to be effective in eliminating short circuiting and damping excessive loadings, although the majority of COD removal occurs in the first stage which retains the greatest quantity of attached biomass. A good quality effluent was produced.     

Denitrification with a bacterial disc unit

An enclosed rotating disc unit was operated anaerobically as a denitrifying system, with methanol as the hydrogen donor. As the bacterial population became established, denitrification rate increased by 1·5 mg NO₃⁻—N reduced m⁻² h⁻², to a maximum rate of 260 mg NO₃⁻—N reduced m⁻²h⁻¹. The C:N ratio necessary for complete denitrification was found to be 2·6:1. Optimum pH for denitrification lay in the range between pH 7·0 and 8·5. Q₁₀ values were 1·38 between 10 and 30°C, −2·66 above 30°C and 13·06 below 10°C.     

Ecology and energetics of slacks in the Alexandria coastal dunefield

This paper summarises information on the structure and function of dune slacks as discrete ecosystems within the Alexandria coastal dunefield. A typical slack, with a total area of 1900 m² and floor area of 8833 m², harbours four dominant species of pioneer plants in a succession spanning 5 years, corresponding to the interval between a section of slack floor being uncovered by a retreating dune and smothered by an advancing dune. Vegetation biomass totals 221.1 g m⁻² and detritus mass 40.1 g m⁻², with 31% and 3% above ground, respectively. Annual plant production is estimated at 190 g m⁻² using a combination of theoretical calculations and vegetative growth estimates. Animal biomass has been quantified for interstitial meiofauna at 1.0 g m⁻² and all arthropod and vertebrate macrofauna at 0.2 g m⁻². Based on estimated decomposition coefficients of 0.5 year⁻¹ and theoretical consumption estimates for the fauna, 14% of plant production is grazed directly (93% by plant parasitic nematodes, 7% by macrofauna) and 86% enters the detritus pool. Of the latter, 2% is consumed by macrofauna detritivores, 63% is decomposed by the interstitial fauna and 35% accumulates to add to the detritus pool. Vegetation succession and production in the slack thus results in a net build-up of organic matter in the sand. This is finally decomposed when the slack is smothered by an advancing dune ridge, thus maintaining a long term equilibrium level of soil organics. These slacks require minimal management as long as free dune movement and limited human access are maintained.