AUSTIN, Tex. -- What do robotic weeding and making baking soda from wastewater have in common? They -- or rather, the entrepreneurs that dreamed them up -- are all recognized among the most promising startups in the Startup Showcase competition at the third annual SXSW Eco conference in Austin, Texas, this week.

The winner's circle, announced Tuesday night, also includes a customer acquisition platform for renewable energy companies and software that helps utilities and ratepayers conserve water.

The Startup Showcase offers early-stage companies a platform for sharing their innovations to a wide audience and a chance to pitch their startups to a panel of judges comprising advisors and potential investors. Each finalists received three minutes to pitch their company to the judges in front of a live audience. Then, the judges could query and test the finalists for an additional five minutes.

Ben Chostner, vice president of business development at Mountain View, Calif.-based Blue River Technology, won over the judges in the Greentech category with his description of his company's computer-aided weeding system.

"Our solution increases production while reducing chemical input," he said. The technology works by analyzing digital images of the crops, using cameras integrated into a tractor, as software quickly differentiates weeds from the crop plants -- making decisions, using proprietary computer algorithms, five times per second. It then sprays a concentrated fertilizer only on the plants identified as weeds, thereby killing them and also providing nutrients to the crop plants.

But vying for the judges' approval was especially difficult in the Greentech category -- which included 12 finalists rather than six in each of the other categories. Blue River shared the top Greentech spot with New Sky Energy, out of Boulder, Colo., which has developed a wastewater treatment process that produces both clean water as well as useable chemicals that are then turned into products.

"We hydrolyze the water and then create products using the chemicals we derive from the process," said Deane Little, New Sky Energy's CEO and chief science officer. These products include hydrofluoric or sulfuric acid from the resulting salt. Using captured CO₂, the company also makes sodium carbonate or baking soda.

Interest in the Startup Showcase grew significantly this year, with many more applicants and 24 finalists, double the number of compared to the inaugural 2012 event. This year introduced two new categories: Cleanweb and Social Impact.

Judges also selected two winners in the Cleanweb category: Faraday, a software-as-a-service tool aimed at helping renewable energy and energy efficiency service providers locate and market their services to consumers, and WaterSmart, a water conservation tool. WaterSmart, based in San Francisco, is already working with Bay Area water utilities to help consumers better measure and manage their water footprints.

Finalists in the Social Impact category included a number of products for the developing world, such as Beyonic, a mobile payment system for entrepreneurs, and Portapure, a portable water treatment system. The top spot, however, went to Sseko. The Uganda-based footwear and accessories manufacturer offers a work program designed to help Ugandan women go to college by matching funds they save through working.

The unusual and compelling thing about SXSW Eco that differs from other environmentally themed conferences is that fashion designers and hydrologists and software hackers all have equal footing. The breadth of finalists and categories in the Startup Showcase reflects this same approach.

While the winners and finalists do not receive any cash prizes, the exposure and opportunity to pitch in front of potential investors is quite valuable, said Little: "It was an interesting and exciting challenge to tell our story in three minutes, but it forces you to get right to the point. The judges were very knowledgeable and asked great questions."