H.W Pearson

Guidelines for the minimum evaluation of the performance of full-scale waste stabilization pond systems

Guidelines are presented for the minimum evaluation of the performance of existing full-scale waste stabilization ponds. It is recommended that 24-h flow-weighted composite samples of the raw wastewater and pond effluents be taken over a 5 week period at the hottest and coldest periods of the year and analysed for BOD, COD, SS, NH3-N, NO3-N and total P; faecal coliform numbers should be determined on grab samples, and algal biomass estimated by measuring chlorophyll concentrations in samples of the pond water column. Pond mid-depth mean daily temperatures and pond sludge depths should also be measured, and local meteorological data obtained. The diurnal variation of pond effluent quality and of dissolved oxygen and temperature with depth should be measured at least once during each sampling season. Recommendations are also given for a more simplified estimate of pond performance in areas where the lack of skilled manpower, materials and equipment preclude the complete minimum evaluation procedure.

Expanding the horizons of pond technology and application in an environmentally conscious world

Waste stabilisation pond technology has advanced greatly in terms of application and reliability and this has come from the wealth of modern research. Pond technology can be designed to meet exacting effluent standards and can treat both domestic sewage and a wide range of industrial wastewaters. They are now very much on a par with other wastewater treatment technologies. A wide range of pond types now exist allowing for flexibility in design and optimisation of the process to meet a particular applications or set of conditions. Ponds can be made to combine treatment and effluent storage and are the best and cheapest option for treating wastewaters for subsequent reuse in aquaculture and agriculture. Ponds can be designed to produce large quantities of algal biomass for animal and potential human consumption and for energy production via methane. Ponds are thus a modern wastewater reclamation and resource recovery technology in tune with current environmental thinking.

Vibrio cholerae O1 (El Tor) removal in waste stabilization ponds in northeast Brazil

Abstract A series of ten waste stabilization ponds (a 1-d anaerobic pond followed by nine 2-d ponds) was monitored for the removal of Vibrio cholerae O1. The anaerobic pond reduced the mean number of V. cholerae from 485 per litre of raw wastewater to 28, and there was then a very gradual removal in the next five ponds, after a cumulative retention time of only 11 d, to zero.

A hybrid waste stabilization pond and wastewater storage and treatment reservoir system for wastewater reuse for both restricted and unrestricted crop irrigation

A hybrid waste stabilization pond-wastewater storage and treatment reservoir system is proposed to produce microbiologically safe effluents for both restricted and unrestricted crop irrigation. The wastewater is treated in an anaerobic and facultative pond (and in a maturation pond if the number of human intestinal nematode eggs in the raw wastewater so require). During the non-irrigation season the WSP effluent is used to fill a single WSTR, and during the irrigation season the WSP effluent is used for restricted irrigation and the WSTR contents for unrestricted irrigation. A typical design example shows that the WSTR is financially viable, with an internal rate of return of 58 percent.

Rotavirus removal in experimental waste stabilization pond systems with different geometries and configurations

Rotavirus removal in waste stabilization ponds is a relatively slow process: in a series of ten ponds (a 1-d anaerobic pond followed by nine 2-d ponds) its numbers were reduced from 1.4 × 105 per litre to zero, and in an “innovative” series (a 1-day anaerobic pond, 3-d facultative pond, 3.8-d, 3-d and 5-d maturation ponds) from 5.1 × 104 per litre to <5 per litre. Faecal coliforms were better indicators of rotaviruses than was Clostridium perfringens .

Enumeration of salmonellae in wastewater by the MPN technique

Abstract A comparative study of the use of double and single strength RV enrichment media for the enumeration of salmonellae by the MPN method was carried out. Of 53 samples of raw municipal wastewater and waste stabilization pond effluents examined 83% yielded higher numbers of positive tubes when the various volumes of the samples utilized for the estimations were inoculated into single strength RV enrichment medium than when inoculated into double strength medium. Extending the incubation period of the XLD agar plates from 24h to 48h at 37°C increased the number of confirmed positive tubes by 1–9% with a mean value of 3%. The effect of the strength of the enrichment medium used on the MPN values is discussed.

Baffled primary facultative ponds with inlets and outlets set at different levels treating domestic wastewater in northeast Brazil

This study evaluates the performance of four 2.3 m deep pilot-scale, independently loaded, primary facultative ponds treating predominantly domestic sewage in northeast Brazil. The ponds contained longitudinal baffles giving different length to width ratios from 3.55 to 32.4. The ponds had mean hydraulic retention times of ~15 days, and mean surface organic loadings of 330 kg BOD(5).ha.d(-1) during the first experimental phase and 375 kg BOD(5).ha.d(-1) in the second. The vertical inlets and outlets pipes were positioned at 1.8 m and 5 cm respectively below the pond surface in the first phase and at 50 cm and 1.8 m respectively in the second. All the ponds functioned as efficient primary facultative ponds but statistical analysis demonstrated no differences in effluent quality for most of the parameters measured for the various configurations of baffles and inlet and outlet depths. All behaved similarly to the unbaffled pond. The only exceptions were suspended solids and chlorophyll a concentrations which tended to be lower for all combinations of baffles with the outlets set 1.8 m below the surface. This study suggested that the longitudinal baffling of primary facultative ponds when using vertical inlets and outlets may well not significantly improve pond performance.

RATIONALIZING WASTE STABILIZATION POND DESIGN: THE BIOLOGICAL FACTOR

ABSTRACT Despite the considerable research effort put into understanding the physicochemical and in particular the biological interactions occuring in waste stabilization ponds their design still remains conservative and based on long established criteria for the efficient functioning of industrial process reactors. The assumption that complete mixing improves treatment efficiency in ponds is questioned in favour of allowing stratification to occur to improve bacterial pathogen removal in maturation ponds and possibly BOD removal in facultative ponds. Excessive mixing in anaerobic ponds is likely to increase the risk of odour release and may reduce sludge digestion by inhibiting methanogenisis. Shallow maturation ponds favour the formation of high pH concltions which promote bacterial die-off and may further assist any synergistic effects between high pH and light. The construction of large ponds is critisized in favour of the use of more, smaller ponds, aligned in parallel at all stages in the series. The stimulation of zoopiankton grazing of microaigae to improve effluent quality is discussed and the use of variable height inlet and outlet structures in all ponds is recommended. The need for operational data on radical new pond designs collected so as to allow detailed analysis of the results fa worldwide application is stressed as a research priority